Limit on the number of troops per hero.

I personally do it this way. I give the main hero ten weekly reinforcements from the town. If he has a specific troop specialization, I give him two types of troops of the same level (for example, if it's Hagge, then both nomadic and war centaurs), and I sacrifice one level, the weakest one in my opinion, mainly giving it to my successor. Plus, I usually choose a suitable hero for a specific town, and if there isn't one, I just put the same ten weekly reinforcements into the town. And as soon as the necessary army is finally assembled, I give the rest to the successor, and I haven't lost a single time with this strategy, although it does take quite a while to wait for those ten weekly reinforcements.