This is embarrassing. It looks like I might have to walk back my first post just a little bit. I was, in fact, able to beat the tutorial without too much trouble. I didn't even have to start from scratch. All I needed to do was load an autosave from about 3 or 4 turns back, buy tier-2 units from my home base (instead of the tier-1 units from the more conveniently-placed wilderness forts) and have my backup hero ferry them to me over the course of a half-dozen turns.
It's a tactic I read about online, but didn't attempt on the first go round because it's absolutely inane. Hero characters are supposed to be these powerful leaders who command armies and have complex rpg-style stats, but any hero past the first is good for nothing but playing taxi for your reinforcements. That's because there's a finite number of xp on the map and only so many troops available per week and a single unit, with bigger troop stacks, led by a high level character is better than two weaker units in every particular situation.
So I learned that I was capable of playing the game the "right way," but also that the "right way" is kind of weak. You've got these wide open skill trees, but only a narrow path actually works. You've got a whole stable of heroes to recruit, but you shouldn't actually use them. You've got a half-dozen monsters per faction, but you should win the game before the last ones are unlocked. It's sad.
However, it's not as hard as I thought it would be. And when you're winning, it's easy to forget that you're not winning the way you want to. I really hoped to be able to play in a dilatory fashion, just getting into random scraps, improving my towns, and gathering up artifacts. If I'm forced to be more focused, well that's just the way it's got to be.
And it's not totally bad. I'm at 13 hours already, and I barely noticed the time pass. On the advice of MoogleEmpMog, I tried some skirmish games and those worked out pretty well, though I only played on a small map that forced an end-game confrontation after about a half-hour. Despite the time limit, it did seem to allow more freedom of choice. Perhaps if I play on a larger map, I'll be able to use the tier-3 creatures. That's all I really want. To have an army of angels, dragons, or legendary beasts at my command.
My interim verdict - Might & Magic: Heroes VI is moderately diverting, when it works. I just wish the state of it working felt less like a tight-rope walk.