As of right now, the buffs stack, which i'm not sure is intended, at 120 kills the heralds have so much melee attack and weapon strength that they perform exceptionally even against large targets, and 40 bonus vs infantry means that anything small gets annihlated. I would suggest nerfing them, since even if the buffs did not stack they still seem too strong, but right now they feel blatantly overpowered

Yes, the stacking buffs are intended because getting stronger by piling up kills is the whole point of this unit's custom ability.
Now I do agree that the maxed ability can feel OP at times but that's pretty much the only thing this unit has going for.
They are pretty much just Chosen on steroids when you think about it: *so most of the counter strategies against your average Chosen unit should still be valid, with or without the custom ability.*
That said, it's also an ability that is very reliant on how you use the unit in battle and against what:
-Piling up 120 easy kills on a Bretonnian Peasant Mob while keeping 100% unit models will feel super OP, that's inevitable.
-Piling up 120 kills after losing 40-50% unit models due to enemy Magic/Artillery/Warmachines/Powerful anti-infantry units may feel still very strong but maybe not that OP at that point.
Anyway, I'm still open to your nerf suggestions but you'll have to be a lil more specific than "blatantly overpowered" and give some numbers I can work with.
But to be honest considering that "since even if the buffs did not stack they still seem too strong" line, I'm inclined to think that we are not going to easily find a common ground here.

>>>*I'm open to eventually tone down the unit a bit, NOT nerfing it to the ground.*<<<

Again, feel free to post your suggestions, and if they look fair, I'll think about it and eventually make those balance changes .

My suggestion would be to reduce the power of death and destruction so each tier has the potency of the first tier. This would leave it's initial power unchanged while making it a little less ridiculous in prolonged battles. At tier three death and destruction this would reduce it's weapon strength from 148 to 118, melee attack from 76 to 61, physical res from 30 to 15, and bonus vs infantry from 40 to 25. They would still beat essentially any infantry in the game even when outnumbered, but would sustain somewhat more damage when doing so, and would be less effective at rapidly killing single entities. I will also note that the ability isn't necessarily the only thing the heralds have going for them, as chosen with 10 bonus vs infantry, terror, and a -8 ld effect on attacks are already a pretty strong ror. This unit is very cool and it is fine that they are strong, I just think a small reduction in power would make them feel a bit less overbearing to use.

Ok, that sounds fair enough to me.
Will make those balance changes .