A prover model might be used as a tool in the coming future.
But a simple way to see it is that when you pick between multiple large models that have different strengths, you have a larger amount of parameters just to work with (e.g. Deepseek R1 + V3 + Qwen + LLaMA ends up being 2 trillion total parameters to pick from), whereas "picking" the experts in an MoE like has a smaller amount of total different parameters you are working with (e.g. R1 is 671 billion, Qwen is 235).
In the future? I'm pretty sure people do that already.
The point being that a separate expert model would be better at its own field than a single model that tries to be good at everything. Intuitively it makes sense, in practice I have seen anecdotes where finetuning a small model on domain data makes the model lose coherence on other topics.
This is expected behaviour.