As with 99% of the posts on this sub the answer is to stop letting people walk all over you and realise you don't have to hang out with people who are actively rude to you.

This is not a dig at you OP, everyone has to learn this lesson by experience at some point.

But this one in particular:

"Summon a Xorn, bind it for x days, dig out a mountain. He also has Simulacrum, so now he can create copies of himself, and by extension summon more elementals. It got so busted I had to tell him to knock it off. "

This kind of thing is an easy solve if you don't want to just outright say "no, this isn't a business strategy game" to your player.

Just have your world act like a world. The king hears someone has been digging their local resources out without a licence and sends forces to put a stop to it.

PCs too powerful to care about kings? It belongs to a dragon or something.