I think most people you ask will say that on a measurement-level QM is a probability theory, despite as you said the deterministic nature of the wavefunctions themselves. They will say these probabilities are irreducible.
Could this be true? Sure. But i also think that's it's a bit naive to completely rule out an underlying deterministic nature to measurements, at least inat our current point in time/knowledge with many aspects of physics being unsolved. Just to be clear, we could be talking about something too complex for us humans to even begin to understand, ie. chaos functions. But like chaos functions, there is determinism, whether we understand it or not.
Anyway i don't think that wavefunctions being deterministic necessarily means measurement hashas to be. I think it's interesting that wavefunctions are deterministic but measurement isn't, but i don't know if it prohibits measurement from being purely probabilistic in nature.