Well what are your priorities? It's a commute, so if you have to arrive a little more dry and less sweaty, go for the lower effort road bike. If you can change at work/ don't care how sweaty you are etc, and like the MTB ride, use that? Another consideration is if your MTB can have a rack, then putting the backpack (if you use one) will also alleviate a bit of the perspiration?
Or dump both and get a gravel bike which is in between the 2? hahaha