The list is endless.
New in the amplifier world is no where near being better in all cases.
Circuit refinements are rare, and the effect on sonic end points that the given amplifier circuitry that is new can deliver -- is highly debatable at best. One can point their finger at multiple (probably hundreds) designs that are touted as new, but are really just refinements of an old circuit design that has been around in the given company for 20 plus years. Where they dole it out by the inch as that is all that can be done to make manufacturing work. Where not all sages and mages in audio work with the same intelligence or speed of mind (and results) and such. Where they can, even if the individual is faster and better than the next, they can only work within the market in the way that the market (buyers) themselves - evolve and grow.
Refining or intelligently rebuilding and re-executing an old design (old amplifier) is most times a better path financial outlay and speed of motion toward the peaks-- than buying a new item. It’s not about spending more but spending intelligently.
It is called the last step in audiophile evolution. Where the searcher and the goal begin to become as one. Which is why it can take so long for some to inch their way toward it. Most never get there. I’m the opposite (happened over time), I’ve gone so far as to be taking $10-20k items apart into a big pile of parts within one day of owning them. So I’ve learned to not buy new in the search for audio nirvana. Too costly, by far. I’ve learned to simply buy frameworks and starting points.
This thing where the modketeer or highly talented technician or ’frustrated designer’ is the best person on the planet to know, if one is looking for audio nirvana. Finding one of those is like finding water in an endless desert. Since it is so rare (finding the right one), few people know a real one when they meet them.
Although many an audio company owner and designer is exactly that, but all with different levels of talent and experience, where they are mostly forced to abandon that path (if they started with it), for the path of development of product for retail sale and that associated world of enforced direction, design, and rigidity...
It’s the edge of the whisper of the Buddhist heights of audio listening evolution that you are catching a glimpse of. You’re just touching the edges of it.
But this is a limited hangout, in pretty well all ways possible, even though it is the actual end point. It’s the nature of how things work. All the new (minimum sales levels required) turning into used (so peaks can be reached) is the only way this can happen. The masses must exist so the search for perfection has lands to walk though and experiences to shape it -- on in it’s meandering path.