I am indeed middle aged. But somehow can still hear up to 15.5K. No idea how that happened, plenty of loud concerts and SPL cars back in the day.
I couldn't hear quite that high back when I had all my hair and Mark Wahlberg was a boy band.
What's the landscape for A/B amps?
100% Obsolete. Most offerings on the market are cookie cutter copies of the same 20+ year old designs made in the Far East. Apart from those, there's a couple boutique (read over-priced over-hyped) brands that are selling some unique and modern designs but the only thing you get out of them will be huge size and terrible efficiency.
This isn't beef or maple syrup where you're looking for grade A and other letters = shit quality. It's just a description of the circuit design and advances in semiconductors over the last 40 years have made it possible to do some amazing things by way of extremely small and efficient amplifiers.
So long as you stay out of the absolute bottom of the trash bin amps you're not going to take Richard Clark's 10 grand, and even many of the budget brand offerings will still have fine sound when used within their limits.
For the most part the USA was priced out (read taxed and regulated) out of the electronics manufacturing market around 20 years ago. If you're dead set on buying American made check out MMatts out of Florida, those are reasonably priced amps for what they are, are their own designs, and generally bullet proof and competition worthy quality. Their mono amps have been class D full-bridge for ages and I suspect their multichannels are going to be as well.