...I am curious, have the AI heroes ever been a problem to you?...
That's a great question, one I've been thinking about.
Short answer is kinda/sorta/not really/no.
-Kinda/sorta: Some champs cast spells. The spells really seem more a problem than they are. Curse, for exmaple -- I hate to have it cast on me but can't remember any time it really caused problems. There's a spell that drains health from all my units, healing the caster. It's caused me some problems, making it take longer to kill that caster, but at the level my troops were at that time their lost health didn't really hurt. If the AI did a decent job of spell use, focus fire, etc. then I think AI champ casters would definitely hurt.
In the early game phase the champs/sov aren't bad, but as time goes on they get less and less effective.
As for AI champ melee types, they don't do nearly the damage as the built-up normal troops do.
-Not really/no: I typically don't focus on AI champs. They just don't do the damage that regular troops do.
The above holds true for Sovs too. They are generally more powerful than champs, but still can't match the damage done by normal troops.\
A further problem is that when killed an enemy champ/sov ends up in a nearby city with 1 health, for 5(?) turns, slowly healing. If my army is on a roll (and it usually is, once things get going) I hit the next city in a few turns, so the enemy champ/sov is at low health. Sometimes they're at 1 health. Even then, I won't usually target them, even tho they're an easy kill -- other, normal, units are too dangerous to put off attacking.
In my current Insane game (same game referenced in the past week's worth of posts) my Sov is now lvl 20. While it's true I spent a lot of level-ups to max 3 spell lines, and haven't spent much gold in the shop to max out his armor/etc. (too darn expensive, even netting 200 gold/turn it's more effective to upgrade normal units than sov/champs), I just use him to cast the following spells:
-haste (very very rare)
My lvl 20 Sov spends tac battles casting basic, low level spells, acting as support. My normal units do the heavy lifting:
This is my lvl 20 Sov:
This is a normal melee unit that I made back in the early phase of the game, partly upgraded and now lvl 14:
Here's a ranged unit from the early days, now lvl 13, mostly upgraded:
This is a newly-made unit, melee, lvl 3, high defense:
Even the newly-made lvl 3 unit has 7x the attack 4x the defense, and almost 2x the health of my lvl 20 Sov.
I try to have 4 melee, 4 ranged, and 1 champ/sov in each army. The champ/sov really only act as support. If they can cast heal, slow, or haste they're useful. Otherwise, unless there's an enemy unit with only 10 or so health to finish off the champ does nothing.
The name of the expansion is Legendary Heroes. Does anyone feel they are legendary in mid to end-game?
How powerful should a champ be? My preference would be someone who could hold their own against a normal, current tech, unit. One champ shouldn't lay waste to whole armies of normal units, but one normal unit shouldn't lay waste to one champ.
If the above is considered a topic to address to improve, suggestions are:
-champ/sov should ramp up faster in power (perhaps more "+1/lvl" bonuses, rather than the "+1", "+2", etc. per abilities?) Also, greater health/attack/defense increases.
-upgrading champs at the shop should cost significantly less, or even be free.