Which AoW do you mean? It can't be the first one.
I don't quite see how AoW 1 has less action, given that in AoW 1 I have plenty of shit to do in the early game, being already busy conquering cities in the first turns, whereas in Heroes 3 my first turns consist of taking sawmills from 50 gremlins and it isn't uncommon to not have conquered any cities in the first two weeks since there are usually like 10-15 or less cities per map, there's a decent chance that I haven't even encountered another city yet.
Coupled with the fact that I need heroes to lead my troops in Heroes and can typically afford to give decent troops to only 1-3 of them (with rest of them running around with 1 troop to scout/collect resources or acting as couriers for my main heroes), I have a very limited number of entities that do anything interesting on the map. Whereas in Aow, although the main muscles in AoW are my leader and heroe(s)/handful of elite troops, I can still typically project my force in more places at once, since I don't neccessarily need a big ass army somewhere to make a difference (often thanks to the stupidity of the AI, granted) and in case I do have bigger stacks of elite troops in once place, I can split them up as I see fit, not needing another hero in the vicinity.
The biggest drawback AoW has compared to Heroes 3 is that while in Heroes, the AI is nothing special, its retardation isn't as painfully obvious as it is in AoW. Once you have a decent understanding of the game, it is too easy to exploit things like terrain, flyers and walls against the AI in AoW, also the AI is infuriatingly passive.