Well, the distinction here, is that I'm NOT looking to debate tubes vs SS. It is in the advances in topology that I believe solid state holds the biggest advances. Witness amps like Jadis or CAT or various SET designs; they sound essentially the same as they have for decades and most tube circuits have been around since the 50s or earlier.
My point is, for me, for over 40 years tubes ruled, and there was no substiute. I was weaned on my dads 50s vintage tube based console stereo, but my last two amplifiers, and I suspect my next will be SS. The gap has closed.
Has SS on average gotten better? Yes. Whether the gap has closed is debatable...
And furthermore, what gap and how has it closed? would people who are interested in enjoying all types of music vs. an audiophile sound take a 20 year old Symphonic Line or older Gryphon over the newer hyped up SS? Heck Yes!
During the same period of time as these SS amps have been improving, the popular speakers have gotten harder to drive.
Audio Research can't drive wilsons or focals unless guys like a syrupy sound. Heck, Audio Research 750 can't drive their own Aida unless one likes syrupy sound.
And while the technology has "improved on average" the audiophiles have gotten sicker, fatter, and lazier to get out of the chair. Just as streaming Tidal instead of playing their favorite record or CD, it's just good enough...