Let's make our own models (and maybe even animations)

I
Please, don't pretend to be an expert in something you don't understand.
Footman-

Let me explain it simply and clearly: the 5th Heroes game was designed in such a way that, apart from replacing textures of existing creatures and creating new maps with simple Lua scripts (although I've seen how they partially changed the graphics with them, but these are terrible workarounds), you couldn't do ANYTHING else.

Well, okay. Thank you very much for explaining it again "simply and clearly".))
No one deliberately "limited" the functionality for modders; it's just that Nival suddenly made a game, not a platform for you to tinker with. In short, all this talk about "technical imperfection" and "limited functionality" is worthless. And I have the feeling that it's only needed for your "armchair" expertise.
Specifically, there are no things that limit your ability to import models and animations into the 5th game, except that you can't upload a normal map, what a tragedy, it's just awful. The moral of the story is, stop whining and pretending to be an expert.

Regarding "primitive" Lua scripts. You call them primitive because you yourself are not "primitive"? In my opinion, Lua is just a language. With intelligence and ingenuity, you can significantly change the gameplay with scripts. Regarding the visuals, you probably made a mistake, saying that they changed it with scripts somewhere. Maybe I'm wrong, but without proof, we won't figure it out.

and why the 5th Heroes didn't fail like the 6th Heroes for me remains a very strange mystery.

Again, your expert opinion. The game doesn't have the ability to display a normal map; how could it not fail at all? A mystery!))
The 5th game didn't fail because it's suddenly a good game. And the presence or absence of some graphical features suddenly has little impact on this fact.

I also really like how you criticize CrazyPill's method, saying that you don't like it, and... in fact, you still use it. Or are you adding models through Blitzkrieg's plugins via the Mart editor?) Plus, what if I tell you that you are not the first modder to add animations to Heroes? This was done a long time ago; check out the English-language thread with Archangel OM, if you're interested.

Firstly, now it's only you, and yes, I won't be shy, I consider myself weak,
...
(I'm not lying, I wanted to make a 3D catapult from scratch from the 4th Heroes, I really liked it, but this idea quickly faded).

I'm not trying to inspire you in vain. But you are wrong again, and you are wrong to consider yourself "weak" in this context. In fact, there is nothing in creating models that you couldn't handle. You and FrozenSoul are quite ready to move in this direction, if, of course, you are interested in it and if you are willing to put in the effort.

This will, of course, be more difficult than whining and pretending to be an expert on the forum. But at least it's objectively more useful and, in theory and in the long run, it might, I don't know, help you find a good job.