The fact is that I have all the original perks, just like the heroes themselves. It would be great to see a list of proposed changes with detailed descriptions of everything.
Maybe it's not finished yet, but with what I have, the Harbingers are on the sixth level. Death Knights, in my opinion, would fit there better.
I myself really liked the Death Knights in Might and Magic III, but in Heroes of Might and Magic V (only after the modification), I liked the Harbingers and Necrodrakes even more.
You change the perks as you see fit, even if they don't fit. While playing, I've seen many abilities taken from completely unclear units – like the "Fire Trap" ability on Zombies. Isn't it too difficult to just swap the textures? It's not even necessary to make the Harbingers flying – just add a cage or two to their movement, for example.
Changing the units is not a problem. But in the area of already made changes (in particular, the implementation of units), I am conservative. Because it's done, it works, and it works very well. The suggestion about the Death Knights came too late; it should have been made and justified at the beginning of the mod, when the core was not yet formed. Instead, I went a different way – I made what exists work, without making changes to the army composition.
That is, I can consider suggestions to change the abilities of certain units or even make simple changes to the visuals, such as recoloring, adding special effects, or changing weapons. But the suggestion to completely remove certain units and replace them with others is too much, it's too late for such radical suggestions.
Harbingers (damage dealers) and Dragons (debuffers-tanks) already work well together as a team; Death Knights can conceptually only replace the Harbingers (I don't see them as debuffers-tanks, that contradicts their essence). But the Grim Reaper looks no less impressive (it's a matter of taste) and is more original than a dead copy of a human knight. Their problem in Heroes of Might and Magic V was weak perks and tactical insignificance compared to Death Knights, which has been fixed.
Try playing a few games as the Undead in Heroes of Might and Magic V duels and get the hang of it – then these questions will disappear, and my objections will become clear.
Added 3 minutes ago
And dragons are dragons everywhere. They've become tiresome after so much time in gaming – they're shoved into every game possible. In general, the most logical thing is to move them all to the neutrals and significantly strengthen them. So that they cause terror in single numbers, like the Azure Dragons in Might and Magic III, and not die with half a hit and fly in flocks of 20-100.