@sleipnersm38 Yeah, I hear you. I think they’re just keeping it consistent with their rules throughout the base game, i.e. bonuses can’t stack. That’s already something they’ve done. For example, defenders/attackers of a city with a river don’t get bonuses/negatives to stack on each other. Same with river and mountain territories, etc.
Just to clarify my example and yours too, a commander could help units on a mountain territory that were defending, but it would be non-mountain infantry units, since mountain infantry already have a +1 bonus. Regular infantry, militia, etc. could still benefit from that commander.