Speaker sensitivity vs SQ

Speakers alone make no sound. Complete systems do. Need to examine the complete system before any meaningful comparison can be made.

My understanding is MC prefers high efficiency speakers because they tend to be easier to drive and will work well with most any amp. There is truth to that. However high efficiency speakers also tend to be large and often expensive. Also bulky and more than many would prefer to have to deal with. That’s why the trend is towards smaller speakers that are necessarily lower efficiency if also extended in the bass. Amp choices for best possible performance are still plentiful but more limited. Many tube amps need not apply.

MC is also a Tekton fan. Tekton does tend to offer larger speakers that are more efficient than most but not as efficient as true "high efficiency" speakers like Klipsch, Avantgarde, Volti, Classic Audio Design, and others. Notice most of those are also large and apply horn/waveguide technology to deliver true high efficiency in something some might want in their homes. Tekton offers good value compared to many for large more efficient than most speakers.

So high efficiency alone can be a good thing but like always no one approach has all the advantages that all will care about most.

Also I gather MCs mindset is real men like large manly speakers that may not be very pretty whereas you are perhaps a bit of a w-ss if you care about aesthetics and how they look in your house. That’s for the wife to care about and the real men to ignore.

At least that is my understanding of how MC thinks, FWIW.

This isn’t an example of my preference but an efficient full range speaker. I guess it would also tick the manly man speaker box as well. I also mentioned the Phantom earlier again not as a preference but what can be done with small enclosures, active crossovers and DSP. I guess these are the opposite. 

https://www.jtrspeakers.com/jtr-noesis-215rt

A low sensitivity speaker can be very bit as dynamic as a high sensitivity speaker. It is just a matter of power.
Has anybody ever wondered by no two loudspeakers sound alike? Assuming there is only one accurate sound, that would mean that everyone except for maybe one company has it wrong. More probably nobody has it right.  There are so many varied considerations in speaker design that it is difficult to be versed in all of them. So, we are left to art and our own devises, hearing. We all have our theories and preferences which is what makes this fun. 
I personally don't care at all about efficiency. I separate sub bass from everything else because the considerations are so vastly different. I care about directivity, uniform radiation and radiation type (line vs point source). Because of the directivity mandate I prefer ESL line sources and horns (point source), one moderately inefficient 89-90dB/watt/meter and one very efficient 100+dB/watt/meter. Both are a much better impedance match to air thus the transfer of sound from the driver to air has inherently less distortion. Dynamic drivers sound rounded off to me as if the tips of the transients are missing (no idea if this is correct or not). Many like that "smoothness" and certainly prefer the size. For many it has been the only type they have been exposed to. 
ESL line source speakers are a bit tricky as they do not conform to the usual rules. Even though they are less efficient, because they project power into the room better than a point source an ESL playing at 90dB at 1 meter will be substantially louder and more dynamic back in the room. Than a dynamic speaker playing at 90dB at 1 meter.
Because small ESLs can be rather timid I am of the opinion that if you are going to do ESLs get them 8 or 9 feet tall (depends on your ceiling). It is a major difference in performance, so much so that a pair of subwoofers will never be able to keep up with them, takes at least 4.
As for subwoofers, we have been blessed with modern drivers, amps and crossovers. With enough power you can make a subwoofer do almost anything you want within it's volume constraints. The real problem is the room. If you have to you use multiple units and keep the crossover below 80 Hz. With some speakers like planar magnetics and ESLs there are advantages to crossing higher which means placing the subs in a symmetrical array otherwise you can put them anywhere as long as they are up against a wall. If you put a sub in a corner it is going to be louder than the others.
Can you make an efficient subwoofer? Sure, I made one, or rather we made two. We put 30" Hartley woofers in 25 cubic foot enclosures and drove each one with 20 class A watts. Ridiculous would be an understatement but it worked. You can not use most modern subwoofer drivers in large enclosures. What happens is the voice coil bottoms out making a very disturbing sound. You could use multiple drivers so that each one sees a smaller volume but you still have a very big speaker. There is this thing now with dipole subwoofers. If you have been mislead to think these work just measure their performance. The data will make you cry. There is no circumstance under which a dipole subwoofer will perform reasonably flat from 18 to 100 Hz. I've never measured the efficiency of one but given the degree of cancelation going on I can't imagine that it will be very good. 
IMHO  full range drivers by themselves do not cut it. You can get a very nice midrange and if you lock your head dead on with the driver some treble and in a transmission line enclosure even a little bass. You can do better with Parts Express, Madisound and a little smarts. Horns are great as they are directional and do not bounce sound all over the place. I love the visual statement some of the systems make. There is nothing cooler than those multicolored and wooden horns. Reminds me of "His Masters Voice" and boy do they go loud. If your thing is pee-watt amplifiers these are definitely your speakers. Good horns will not honk at you like PA speakers and like ESLs the micro-detail and transients are excellent as both are much more efficient at transferring sound to open air. Listen to a drum solo and those snare drum snaps. 

OP, you are correct, the John DeVore video does not answer your original question. And for me it is a useful tool to dig deeper into your question. So, why don't manufacturers make efficient speakers? You might want to next ask, how do we determine if a speaker is efficient, what's the difference. And the video helps us understand that some manufacturers are not giving us an honest real world picture with their specs that we can rely on to make that determination. In other words, there are more hard to drive speakers for sale than an arbitrary cut off db number might tell us. I hope you will feel at some point that your question has been answered well enough. And then at some point you may decide you want a new speaker efficient enough to meet your needs. Caveat Emptor, we need to do our homework and not just rely on the published specs. 

Has anybody ever wondered by no two loudspeakers sound alike? Assuming there is only one accurate sound, that would mean that everyone except for maybe one company has it wrong.

Sorry but this is completely non sensical...

First "accuracy" is a complex chain of measured numbers, for example in the standard processing of designed pieces of electronic components, but "accuracy" in this sense had "no audible signification" except to certify that a piece of electronic component was rightfully designed....

Then the "accuracy of a sound" is in no way synonymus with the accuracy of an electronic design pieces or the accuracy of the audio system and the accuracy of sound is never reducible to them for his only source and cause...The "accuracy of sound" is a phenomenon mainly linked to the relation between the audio system and his embeddings linked to the ears/brain evalutation...

Then "assuming there is only one accurate sound" is a sentence with absoletely no meaning....And accuracy of a sound in music, is not accuracy in the acoustical sense...Timbre for example is not reducible to tone accuracy only...The accuracy of a sound produced by an electronical design in a laboratory has nothing to do with the accuracy of a sound in a room...

The sound did not come from our speakers to our ears directly in a pure delivery without any noise from any source, but on the contrary is the results of a complex acoustical interaction with the room....More than that the audio system is immersed in the mechanical dimension, in the electrical dimension and in the acoustical dimension, then the sound coming from our speakers is the signal/noise complex chain that is modified by these constraint i called the 3 embeddings....


Then your conclusion is also totally absurd because saying that all companies have it wrong is , like someone who want to recreate the wheel, especially, a non circular wheel....All company have it all relatively right in the limit of the trade-off implicated by electrical and mechanical constraints in the design of speakers and the choices they made...There is no perfect speakers, there is some better than others for some ears and for some goal....

Sound quality, timbre experience, imaging etc all these qualities come from the audio system in his totality embed in a specific room , in a specific house, and in a specific electrical grid..

Someone who think that human experience of musical sound come from the speaker design mainly is beside his shoes...

Why there is no 2 speakers that sound like each other?

The list of reasons is so numerous that reducing it to  difference in electronical design and mechanical design of speakers is very misleading...

But in audio thread the electronic design importance veiled for most eyes/ears the importance of the embeddings...

A piece of electronic design cannot work optimally in a non controlled environment.... Is it not simple?