Yes and Audio Note would undoubtedly the best example of this way of thinking. My experience with valve amps is certainly in agreement with the fact they start to harden up the louder they were played, switching from Class A to AB when things got going. It‘s very unlikely I will ever venture back to tubes but my money would be spent on Audio Note kit if I do.A quick browse of the thread - I don't see anyone mentioning speaker sensitivity for lower volume listening. The OP refers to valve amps - but generally speaking one has to partner a valve amp with a speaker that's got a higher level of sensitivity for a successful outcome!
For example a 15w tube amp wouldn't be able to drive reasonably a set of bookshelf speakers at 85db or floor standers at 89db sensitivity.