Limit on the number of troops per hero.

Have you tried recruiting both types? Honestly, if you recruit both, you get a very powerful force. I've personally seen this with Orcs, Humans, and Sylvan elves. I haven't tried it with the others yet. But I agree about having a specific goal in mind. After all, many will wonder why an Orc should downgrade from level 6 to level 2, even if the hero has a specialization. That's the question many will ask. But I only do this as a minimum at level 25, and that's why my Centaurs become many times stronger than Wyverns. That's why I change them. Besides, it's very convenient. In short, this is just my point of view; I can't vouch for others.
And yet, this makes the game more interesting for me when playing against other players.