> Would you really say that the main part of non-determinism in LLM-usage stems from this
Yes I would because it causes exponential divergence (P(correct) = (1-e)^n) and doesn't have a widely adopted solution. The major labs have very expensive researchers focused on this specific problem.
There is a paper from Thinking Machines from September around Batch Invariant kernels you should read, it's a good primer on this issue of non-determinism in LLM's, you might learn something from it!
Unfortunately the method has quite a lot of overhead, but promising research all the same.