[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.