Have speakers really improved within the last 20 years??

The OP seems rather ludicrous.

What’s the definition of “most speakers”? Many/most audiophiles distinguish differences between high-end audio gear vs box store main stream products which garner the vast majority of speaker sales. So are we comparing current vs 20yrs past consumer box store speakers? What’s the point? Why bring up on this high-end forum?

Consumer box store speakers have to keep costs low in order to compete in a very crowded market. If costs go up, then either profit margins suffer or have to pass on the cost by raising the price which may price them out of the market. Therefore, R&D including material science expenditures are kept low. With limited R&D you’d expect limited results, not sure what the OP was trying to say/prove.

What “measured performance“ data for 20yr old speakers is available for comparison to current speakers? For “most speakers” ~ box store speakers, you’re lucky to find any specifications and if you find any, the specifications are simplistic/rudimentarily unlike high-end components. What’s the point of comparing simplistic/rudimentarily specifications?

Why bring up the subject of “most speakers” on this forum? I surmise that most/all on this forum are audiophiles interested in better content and/or better audio chain performance. We could care less for average box store components comparisons, rather, we’re after a deeper connection to the music often through better components.

Poko and reven, you’ve got it right. The early posts might have had some zing with all the pomp of being the self designated and worlds only true expert and judge of everything audiophile. Now it’s just boring repetition of the same ideas and subjects that by their nature cannot be determined, or as the self proclaimed judge, he disputes any facts as non factual. That’s why I have now proclaimed myself as the one true expert and judge, he let his credentials lapse. Lol. Though out of kindness I have deemed that he may still have complete control and and final say in his own home. ( which of course is exactly the same level of power we each have, just don’t tell him, I like him believing I’ve made a special consideration for him) 

It depends on what type of speaker.

Quality stand-mounts -yes, for a price. The good ones are north of 5k. Cone-material and cavity-noise were improved.

Big-box cones -slow improvements, I’ve noticed better driver-integration -3 -ways were a tough-nut to crack. If you can afford the pricey Magicos, then progress was more than "slow".

Panels -less panel-resonance and better bass-integration,

Horns -the biggest improvement. Esp. for those who were not tweaking before (to remove mouth reflections). If Emerald Physics and Spatial count as horns, this category did very good.

Sigh--on and on we go--yes, Kenjit, you have the right to believe that measurements are the only way to know if a speaker is good or has improved over the years.  But your obsession with measurements is misplaced--why?  Because your ears don't process sound the same way a microphone does.  What a microphone hears, and measures, is nothing like what your ears process and filter.  Therefore, relying on measurements is pointless--it's only a first step filter to weed out really bad speakers with poor FR--which your ears could do anyway--after that it's up to your golden ears entirely--and merely your opinion...

Short answer:Yes.
Long Answer:Yes.