/snip
Again, my choices are: 1) never play in or run a game, or; 2) deal with players like this. There's no 3.
Are you serious about wanting this to change? Because, honestly, from a totally outsider point of view, the only common element I'm seeing here is you. Which means, again, judging with very little information here, that it's possible that you might be part of the problem. It sounds like you've gotten into this competition loop with your players and somehow it just continues to escalate every time you play with any group of players.
So, here's my totally unsolicited and poorly thought out bit of advice. The next campaign you run, just say yes. To everything. No matter what. Player wants to play a jedi in a bunny mech suit armed with pocket nukes? You say yes. To everything. Don't try to manage balance. Don't try to manage anything. You run whatever scenarios and campaign you want to run, but, whatever the players ask for, they get.
I submit, that after a very short adjustment period, the players will stop pulling against you and resisting you. They will govern themselves and each other FAR more effectively than you ever can. Give them 100% of the power over breaking the campaign and it becomes astonishing just how self-limiting players will become. They will be far, FAR more aware of game balance than you and will act on it.
I know it's not an easy thing to do. But, it's worked for me very, very well. I actually wind up being the one to suggest more powerful options to my players frequently. One player wanted an owl folk in my latest campaign and another player objected saying flight was too powerful. I didn't really care and said yes. And, funnily enough, the character hasn't dominated anything. Totally in keeping with the rest of the party. Having flight has mattered in a couple of scenarios - but, overall? Not a big deal at all.
Players are far, far more self-regulating than you will ever be. But, if you TELL them that they have to regulate, they will resist you to the end of time. Tell them to go left and they'll go right, just out of spite. But ask them which way they want to go and they'll almost always go the way you wanted them to go in the first place.