is it a wrong assumption that start ups don't provide enough design problems to back end developers?

I dont think so. Most startups have a very pragmatic approach in the beginning hire bunch of juniors and build first refactor later. Give it couple years and at best case you will be walking into a refactor party worst case you gonna have to nuke whole backend

Damn I always need to think a couple more times when the question is negated and the answer is double negated 😆

So, @zemaitis thinks it’s a correct assumption.

Good that I dont have to work with OP's code

I've been in a few start ups and they suffer from rushing to much to deliver. a good back end has to be structured and planned and that takes time. usually what you get is a lasagna. front end is harder not to see if it's broken, so people (specially non devs) focus more on that.