No offense, but complaining about the "limitations" of Heroes 5 is just whining. The ability to import models and animations into Heroes 5 exists; there's nothing that limits your ability to create these models and animations, rather than stealing them from another game. Everything else is irrelevant.
And by the way, there was never a time when modding for Heroes 5 was particularly "more active" than it is now. Believe me, I've been following this topic for about 10 years. From a visual point of view, you can see for yourself what kind of "masterpieces" people created when modding during the "golden age" of Heroes 5 modding. It's really impressive, isn't it?
I meant that if this possibility had appeared not 2 years ago, but had been available from the year the game was released, the situation might have been different. Otherwise, you can only list what you can't do: create your own unique ability, add a new type of animation, such as "defend" which appeared in Heroes 6, create a full-fledged boss (without technical bugs and developer shortcomings), like Arriban from the same sixth installment, use vertex maps, and I would have liked to remove Gloss due to its flawed implementation, and you also can't create your own effect (it would be more accurate to say you can, but you can't export it into the game), and so on.
Regarding mods from the golden age, I've seen very few of them to judge, either the links are broken or there are no screenshots at all (I only remember griffons with open helmets).