Road shoes vs mt bike shoes

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.

When you come up to a stop light and put a foot down with MTB shoes you're far less likely to have your foot slip out and dump you on the ground and then have all of the surrounding people act really concerned and then split a gut afterwards. So by using SPD MTB pedals you could be saving the lives of all of these motorists who could lose control of their vehicles from laughing. And yes, in my 40+ years of riding I've probably killed a dozen drivers before learning how to put a road shoe foot down in all conditions.