Yes, tying up skeletons in melee is a lovely thing:) By the way, that's where I love to send in gorgons — at least there they can actually kill someone:)

And you'll only get double on large maps. Necromancers have this cheat-like transformation into undead... what a terrible imbalance! Ideally, only humans can oppose them in this regard by upgrading their troops one level higher.
Let's imagine such a situation: you have a mage town and you've just captured a town... for example, of dark elves. What to do here? Combine them? In my opinion, it's not worth it, although, of course, you can try... Buy and start leveling a second hero? You could, especially if the map is large, but I still usually prefer playing with one combat hero the old-fashioned way.
And for necromancers, everything is simple — you buy creatures there and transform them into your own. Beauty! Thanks to increased income, Knights can upgrade peasants into archers and swordsmen into monks.