I don't blame anyone for stuff like this as a canary, but if you want the M&Ms, you had better be worth the M&Ms.

if the business agreed with the contract then... that's all on them? they didn't have to take the job.

Yeah, we agreed once, but nominally you would prefer to have repeat business. I assume that there are venues that either buy pre-made no-brown-M&M mixes or just don't book bands with that clause.

Van Halen got away with it because it's Van Halen.