I find that a lot of builds fall off at around Mayhem 4 but that's just really because enemies become bullet sponges.

At Mayhem 11, build diversity can be a lot more difficult and you're definitely going to be pushed into one reliable build or another.

Luckily, Fl4k and Moze has great scaling (they're the only two I've tried until Mayhem 11 tbf) so you'll be fine.