I don’t think I’m the one assuming a lot of stuff

Nobody said “hey, maybe turn down the murdurhoboing?”, they chose to trick the players into attacking a god.

2 assumptions here, one that "nobody said..." and also one that the DM "chose to trick the players".

More importantly, there's your implicit assumption that a chaotic murderhobo party facing bahamut in disguise can only be the result of "things going wrong", that "someone" is making the experience bad for the DM. This is pretty clear from this bit:

Step two is removing a player from the game, possibly yourself

And how you're replying elsewhere: "if it's bad, just leave". To reach such conclusion you have to assume that:

• "something is going wrong"
• nobody talked about it out of the game
• nobody did anything else to try avoiding the "wrong" situation
• there were zero "warnings" (nothing else happening in game could be said to be a hint of escalation of a problem to godly level)
• all players are completely oblivious to any traps or tricks the DM could set up
• setting up bahamut in disguise like is meant solely to kill the characters, ignoring the many different possibilities as to why he could show up ("teach a lesson", give a warning, setup for plot)

There is never enough buildup to justify introducing an OP enemy to guaranteed kill your players as a punishment. Even if there was, you should have left the game long before that point, and should leave the game now instead of firing that big gun.

Just because you cannot think of an escalation that leads to a god showing up in a game doesn't mean that nobody else can. Just because you can only see this setup as "rock falls, everyone dies" doesn't mean that everybody else will use it exactly for that.