If you are already a "fully developed pro" or whatever, where you don't need to actually really learn anything new, then sure it doesn't matter what you play through...This is part of my point too - a good-sounding practice amp is a nice luxury, but not necessary. It's easy to get wrapped up in finding the perfect tone for practice, but that's not really the point of practicing. Get something that sounds good enough and is easy enough to use that you want to practice and have fun at it.
But I still need to do major work on every aspect of my playing, including ear training and tone shaping. I can't just go through the motions and expect it to be good enough at a show. I need every moment I can get of practice on all of it - including getting good tones.
I wish I could get into a band that spends more time rehearsing so I could practice in a real band situation but that's not something that anyone seems to do anymore. If it doesn't pay then nobody wants to play.