Ive built almost exactly a duplicate circuit to the later 303, and believe me, if you push your frequencies up beyond the usual 1Khz, and look at distortion at say 1W output - which is still pretty loud for most people with good speakers - you will find its there allright.
Its inherent in any class B design that fully switches off bipolar transistors ..
The solution is to never quite switch them off or better still, use FETS. (or valves!)
My design accomplished the former, but temperature stability was hard to achieve. Technics ripped that (my) design off and integrated the bias stuff into a large hybrid output chip. Nice if you have a tame chip fab plant.
But by the 80's power FETS N and P channel were available, as were much faster output transistors..so any of those plus a bit of careful design could get you an 'AAB' class amp* that really worked bloody well.
- or whatever silly nomenclature they used to describe it.
I only played a bit with power FETS but the initial circuit I breadboard looked amazingly good. very little X over. at all. In fact sub 1W the thing was all class A anyway.
Hence my assertion that a top class tranny couldn't match a bog standard valve amp till about 1980, after that easily could, and there was no excuse to make the bloody things basically so that all imperfections were totally inaudible. At which point the HiFi buffs had to reinvent themselves as magicians, not technicians.
Then the imperfections were in the disc pickups, and the loudspeakers, and in early CD players whose D->A convertors suffered 'orrible X-over distortion. Oversampling and better design fixed that by the 90s.
Essentially there should be no real difference between any quality amp post 1980, in actual sound quality.
And to be honest, a well built valve POWER amp is probably better than any 60's or early 70's tranny amp. You can get better noise out of a tranny disc pre-amp tho. Not that anyone uses disc much.
My cousin, I believe, is still manufacturing valve amps..seems to make a living. Haven't seen him in 45 years..