I stuck it out in one band way beyond the pale. When you have two of the same instrument and one musician is older and has been playing longer but the other guy is better in every respect: I took a hell of a lot of chip-on-the-shoulder sniping about my playing, none of it valid according to the rest of the guys but none of them ever stood up for me. I became bloody minded and made sure I gave the other guy no ammunition whatsover for one of his spurious jibes, then, once he realised and gave me some respect..... I quit and left them to understand how much I was adding!

I did make sure that I didn't leave them in the lurch, though.

Recently, in a group of four, one musician dominated since he was always too busy to practice, so he brought along his material and we were accompanists, sometimes one or more of us not getting to play "his" arrangement.

It didn't take long to realise that the rest of us can and do practice, so now we do much more stuff led by the other three individuals (or pairs etc.), and our former leader can fit in with our arrangements, too. It has put the ego into check and we are playing together again, strangely enough.

My advice would be to have more than one musical project - solo, maybe a duo as well as the band. Gives you a fallback position and hopefully you'll enjoy most of the activities most of the time, which will make tough times in a band more bearable until you can make a well-timed exit or things improve. If the band doesn't want to go your way, try your arrangements or material with another outfit. If the band want to treat you like a session sideman, act like one and find another outlet for your creativity.

I'm not suggesting you do not leave the band, just pick your moment if things don't get better and do it with the minimum of acrimony. You never know when you'll need one of the others in the future.