I think that is a great idea, because it would improve the balance and adds more options.

You misunderstand. The NORMAL limit would be 1 unit (such as Champions) can kill ONE UNIT in a group, not something like Overpower. It's something I suggested as well and it would greatly deepen the game's tactical scene while making sure that armies are primarily fought between armies instead of lone assassins destroying everybody. Great warriors will still be able to do their thing if they specialized in it, although it wouldn't be given right off the bat.

I think he just means the champion does 100 damage to one unit out of the pack at a time. So if it is one champion versus 3 groups of 5 wildlings, then the champion will have to do 15 total attacks to kill them, instead of 3 attacks where each is hit killing a whole wildling pack.

Right. No matter how much damage a champion does, they can only kill one figure in a unit at a time unless they have a skill, item, or spell that increases the number of figures that can be attacked per turn.

I like this idea, especially if it gets applied to non-aoe spells. Right now, champions are just way too efficient compared to units. If bringing an army of champions limits the number of attacks you get, without these traits, then those champions are at greater risk of damage, which should hopefully give units a bit more of a reason to be in the game.

Right now champions/sovereigns are overpowered, being able to kill whole groups without a scratch., for example Magnar wiping 5 Iron Golems by himself.

It's Elemental deja vu, one champion with the 5000 gold sword and the magical plate armor murdering everything by himself.

This exact idea has been thrown around since WoM.

Not sure why they have never gone this route. I like it.

This would be an enormous nerf for champions.  And it's not going to happen (though perhaps it could be a mod).  For a refresher, this is what the game's designers want champions to be like.

High level champions are designed to be able to solo armies.  This isn't an RTS with rock-paper-scissor style counters.  The proper counter to a high level champion is a high level champion.

Frankly, I think making champions more realistic would be boring and kinda besides the point in a game with magic and dragons and whatnot.

FE is the game War of Magic was supposed to be, so I don't see how the Sauron thing would be less influential now.  WoM's problems were legion and iirc, one of them was that champions were underwhelming compared to trained units.

Defender, Warrior, Assassin, Mage... but we have those classes and they work the way you're describing.  The problem is that the level of your champions is so much greater than the level of your opponents that it doesn't matter what you do because your guys are invulnerable.  You've made your champions into demigods; which is pretty much the point of the whole game! 

Of course, if you've outclassed your opponents to the point that there's no challenge then that's boring.  I fail to see how making it take seven extra turns to finish off a unit will make it more fun.

Perhaps you should play on a harder level of difficulty?

I do think this does highlight an issue with the AI, though: it doesn't really understand how to use spells or use units in combination in the tactical battle.  It's battle plans are basic and wrong-headed, (e.g. focus-fire on the weakest and least threatening units) and it completely fails to use its magic effectively to undermine your strategy while enhancing its own.  For example, if it slowed and shrunk/withered/cursed your champion, that would give its regular units a chance to apply a beat down.

Making the AI smarter is a huge challenge, granted.  But I highly doubt nerfing champions is the solution to making the game more fun.

Champions are too powerful because they are allowed to level too much. This would take too much extra code to be feasible for the devs or modders. It is an interesting idea though. I just think there are better ways to equalize the two types of units. 

I highly doubt this is true.  There is already code describing numbers of units. 

That code does damage per unit, not limit damage to one unit. Totally different concept. The balance would further be shifted from this idea. The more you get unit size increased, heroes become weaker. So you would have to add abilities for heroes to kill more than one unit, essentially limiting the whole concept to the early game. The idea is changing a core game concept to fix a problem with hero power and weapon balance. It is one way to go, but not the simplest or most elegant.

Oh yeah, I forgot that the vanilla game has a huge imbalance in equipment power. I shifted that power to levels and made it take forever to level. Nerfing equipment solves alot of unintuitiveness in the game. This also helps with the fact that AI heroes don't buy and equip from the shop, since most of their power comes from leveling.