In simple inexpensive amps perhaps the tube can get you somewhere better and more sophisticated. But for carefully designed high end amps, the tubes are chosen for availability and general character and then the rest of the component is designed to achieve a very specific sound. The goal is the specific sound characteristics… and all the components are chosen to achieve it ...
I think that's true. It means that with gear such as ARC, you're most likely to get a neutral sound. If you want to fiddle with tubes and use them as a sort of EQ device, that's fine. But then modern tube gear such as ARC probably isn't for you.