An interesting idea, but the focus should be more on slowing down the hero growth as that is the main issue here.

Here's my follow-up questions to this exercise, because I think it's a good one.

Do you want leveling to progress at approximately the same pace across all levels?

Should low level units gain levels faster, or higher level units?

How would xp-to-next-level be calculated?

I am guessing some of this is moot until +1/level is nerfed and the same to Path of [Class Here]. Nice to see some passionate posters though! 

The sooner we start talking about these things, the more ideas the devs have to put on their whiteboards at Stardock Central. 

This is kind of a side issue to hero level speed, I agree, but it does address using high level units to power level others.  Especially if the experience is doled out to every participant as it does now.  Having the maximum number of units in a battle effectively multiplies the net experience gained.  This is the opposite of the desired effect in my opinion.  Experience is a reward for risk.  More units = less individual risk, not more.

Distributing experience by levels could potentially accelerate level gain of the higher level units if there is not an appropriate increase in the experience per level (which there should be).  No it wouldn't.  Dragging other non-combatants along to level them would slow your leveling, because you would get a smaller piece of the experience pie.  Mmmmmmm pie 

My answer to the question would be: No, units should not level at the same rate across all levels.  It should take longer the higher you get (thus effectively producing a VERY soft, natural level cap), but that is a matter of exp\level, not exp distribution.  The two need to be considered together because if one is off, it will throw the other off one way or the other.  The current flat distribution heavily favors low level units and makes power leveling possible, which I consider bad.  The multiplication of experience across all units makes crafting a reasonable level gain curve even more difficult.  I would suggest arriving at an acceptable exp distribution that will prevent power leveling, then tune the per level experience cost to achieve an acceptable rate of leveling.

it isn't levels.  It's too easy to get gear.  Buy it in a town,   or go raid the random spawn unprotected huts.   I'm going to continue to compare to mom, because it worked there.  So here it is.

In mom,  you didn't get very good gear from anything you didn't have to fight for.  your  one lone hero couldn't solo a goodie hut  that had more than mana crystals or gold.  You had to build up troops for him to take to the goodie hut to get an artifact.   here we have many more artifact slots.   In mom you had 3. you couldn't just keep adding up all the crappy artifacts to eventually make you godlike.   You had to chose weather this item was better than what it would replace.  As was stated, even with mundane weapons our heroes are too powerful too early.   For the combat formula,  strength is far too easy to come by on skills & gear for heroes.   It should not be an option on gear, and the number of skills offering it should be limited.  The 1 strength per level skill should be 2 picks instead of 1.

MqPiffle states a rule I find myself agreeing with. The total basic amount of xp, a specific encounter yields, should be constant.

That means the model I proposed on page 3 isn't viable. Luckily DexCiscos model is sound and would yield the results I was aiming for - linking xp to risk taken. DexCiscos model would make me use low-level heroes to hunt darklings, and high-level heroes to hunt dragons, instead of just having a single stack of doom, where you have spectators earning xp.

Just splitting xp evenly would be a good start, but in my opinion, it would still favor the stack of doom strategy to heavily.

Besides the xp issue there are two other really big issues that needs fixing regarding heroes.

1) They break the economy. In my last game (Military victory on a small balanced map on normal difficulty in 24 years) I put the tax rate at zero in turn 1 and I never raised it, nor did I miss having gildars at any point in the game. It should not be possible to run a loot driven economy. At most, weapons and artifacts should be sellable for minimal amounts of gildars (or iron, or mana or crystals), i'm thinking 1 to 5 units pr. item at most, unless the item was specifically meant as a monetary reward (stuff like wolf pelts and spider eggs).

2) There is only one viable strategy for how to utilize your heroes, send them adventuring. Different strategies should be viable, hence there should be incentives for keeping your heroes in your cities. This issue is of course linked with the problem, that your cities aren't in any real danger from monsters. However, I personally also think that heroes should be able to contribute to your nation building when stationed in cities, to a much larger degree (a mage could add research when stationed in a city, a warrior could add xp to trained units, a defender could add xp to garrison units etc). 

What if a hero could only hit 1 member of a stack until he built up some skill or weapon that allows him to hit multiple. this would make building troops more important as they would be able to hit multiples in a stack since THEY Have multiple in their stack. Ive noticed most npc only stack up 3 mabey 4 for wolves so mabey a pasive skill say FOLLOWTHROUGH I , II , III . Untill you build up that skill your hero would be less eficient mowing down the rifraf. OR make each stack get bonus dodge checks = to howmany in the stack and cut off the damage at the last dodge so say a stack of 3 5 hp each and 3rd guy dodge then only 10 damage. this would make bringing multy stacks more valuable and make  a hero alow down on lucky or dextrus oponents. 

1. Today? its been like that since day 1 of WoM

2. What do you mean early game, melee heroes / sov rule from beginning to end.

Because regular units aren't terribly weak, they're just badly overshadowed due to a handful of issues that make heroes ridiculously good at everything, plus aoe magic spells dealing multiplied damage to multi-figure units.

End result is heroes are good against heroes, monsters, and units.

They're nerfing a few things .76, I'm waiting to see how that changes the game before posting some more suggestions.

because regular units are not so weak, they are good, just too much easy to freefarm with heroes lead to very powerful early mid heroes while to get as good units you need a ton of research

also i find research quite slow, even with 4 5 cities to get the highest tier of research takes really too long, basically it take the time your hero party can kill the whole world:D

thats another problem

heroes are self sufficient while army need research and resources

and most of all like i told 20 times they are immortal, so cant really have a so strong unit with high reward in playstyle and no risk at all