Depends on the model.
Often the more expensive MTB shoes are the same build as the road shoes. My Lake Winter shoes and my Sidis are like that.
The only things they change is the drilling for the cleats, and the presence/absence of a treaded outer sole,
With these, the difference is very small between road and MTB.
Heavy, or very strong riders can sometimes feel the sole flex a little differently as the road cleats do spread the load a bit wider.