Ruin Explorer
Legend
Yup this really renders the problem non-solvable. We've seen this before - if someone won't set out either the parameters of their actual problem, nor even the parameters of their desired resolution/outcome, then it's impossible to give actually-useful advice.Without knowing more about the game or how exactly these supposed "jerks" are disrupting it with their optimized characters, it's a bit difficult to provide any useful advice, given that the standard advice of "talking to them" was rejected out of hand.
This is a reasonable solution. Whilst I wouldn't play in a 5E D&D game that did that to that formal degree because I'd be concerned about the DM's mindset (I would in more break-able system like GURPS though), I think some people would, and it's likely most/all of the players will go along with it if they're enjoying the campaign and respect the DM. It does rely on the DM being competent re: this kind of thing but the internet/guides can supplement or replace that knowledge. My concern would be that the DM actually has concerns that are so severe that completely basic options that he doesn't feel he could disagree with are causing the "problem" but given he won't release the relevant information, we can't know. An alternate and equally-useful outcome would be the entire group telling the DM that he is being unreasonable and they don't see any problem with how things are. Perhaps hearing it from them he would accept it? If not this will certainly bring things to a head!Here’s something to try that might work in the given parameters. Tell the whole group that because of the issues there have been with party composition, you are going to have to individually approve each character as well as level up decisions.