Loudspeaker sensitivity and dynamics: are the two inexorably linked?

Speakers are just motors and should be treated like motors, but there are a few things at play. 
 

#1 power to weight of the amp/cone is key. Resistance of the drivers play into the power equation as does box size.

#2 air cupping of the driver. Larger drivers (or multiple) move more air with less distance traveled making them reach their peak throw need for a given SPL much easier. Also direct radiating tweeters are 2% efficient as they cut through the air where a good horn is 20% efficient as it has air more or less pressure loaded in front of the driver. 
 

#3. This one is just a guess as I am not sure. I think dispersion matters too. I think narrow dispersion speakers tend to be more dynamic all things being equal (sensitivity, surface area, etc.). Say a wide and narrow speaker of the same efficiency are given one watt instantly. The wide dispersion speaker dumps that energy into the room more than the narrow dispersion speaker. The narrow has more intensity on the leading edge of the sound. Think of a flash light with a focused lens vs no lens at all. Straight on the one with the lens is much brighter while the total brightness of the room when averaged in the same for both. Again just a theory.

While there is perfect correlation, it does generally hold that efficient speakers are subjectively dynamic.  The reason often given is less thermal compression.  With efficient speakers, far less current runs through the voice coil for a given sound output.  That means less heating of the wire.  As wire heats up, its resistance rises so the current flow is reduced — this means compression —the flow is not proportional to what entered the speaker.  Lower current flowing means less thermal compression.

Yes, it is real. High efficiency speakers have a special liveliness all there own. Robert Harley commented on this characteristic in TAS a couple of issues ago in his letter from the editor. Matching these speakers with an SET maximizes this quality. To me the leading edge of the notes seem more clearly defined, not in a harsh, solid state way but in a natural way so that the images seem more lifelike and more three dimensional.

I understand the OP's take. Speakers with higher sensivity db ratings do tend to present a livelier sound. However I am experiencing that in a different way now. Since I got the Loki max from Schiit, I can now raise or lower the db in six different frequencies and if all frequencies are raised, the dynamic presentation is at least doubled of what it is when unaltered. Pretty amazing. And you can tone it done if needed just as well. Enjoying the heck out of all the possibilities, specifically for poorly recorded music.

In my experience with two channel audio, dynamic range is a function of both efficiency and power capacity. When high efficiency and high power capacity are combined, the result is the wide dynamic capability of a loudspeaker. Also having a flat frequency response, flat power response, excellent directivity, very low power compression, wide dispersion and low distortion will contribute to the loudspeakers realism of a live performance at high and low levels. See articles below: 😎

Mike

https://www.linkedin.com/pulse/power-compression-vs-thermal-distortion-loudspeaker-alexander-wilson/

https://mynewmicrophone.com/full-guide-to-loudspeaker-sensitivity-efficiency-ratings/#Loudspeaker-Sensitivity-Vs.-Efficiency

https://www.thebroadcastbridge.com/content/entry/7125/loudspeaker-technology-part-2-the-time-domain-and-human-hearing