[exabrial]

There some truth to that, but not always.

Ideally you would want each time to be fed with a noise free constant current supply. Having each tube on its own power supply would be incredibly expensive but sound awesome.

Buffering the output of each tube would prevent blocking Distortion, but would also be fairly expensive (although now we have mosfets that can handle 500+, so that might not be as bad).

Split audio path about, where the bass goes through cleanly and the treble is overdriven would also sound incredible, but be expensive.

Designs end up being about compromise: the above features will add $5-$35 to the bom per tube, and in the end, a lot of people just end up buying on brand.

My Laney Lionheart L5T has a really cool preamp that uses solid state surface mount components where they don't affect the signal. This drives the bom cost down but sounds incredible (fully buffered fx loop, fully buffered reverb tank).

[i_am_proteus]

And further counterpoint: some guitar players like the sound of overdriving a tube power supply (the attack on a loud note reaches current limits for the p/s rectifier tube, dropping rail voltage, increasing harmonic content). Mesa "dual rectifier" amps made this an option, letting players switch between tube and solid-state rectifiers.

There's definitely room for "improving" guitar amplifiers; I personally think that many guitar players like classic sounds, buy on brand as you said, and the brands just try to reproduce classic designs with any deviations made for cost more than for any other reason.