HoMM VII Haven Units – Haven faction units from the seventh installment of Heroes of Might and Magic.

I also used to try to clean up the model's skeleton from the 6th game and adapt it to the skeleton from the 7th game, but it was too long, tedious, and poorly done.
I think it's faster and easier to just take a model from the 6th game and re-bind it to the skeleton from the 7th game.

Added 1 minute ago

There's no desire or time to do this, at least for free...

Just out of curiosity, how much would you estimate this work would cost (adapting a model from the 6th game to the skeleton from the 7th game)?

Added 6 minutes ago

There are a lot of obstacles left by the developers of the 6th game, in the form of illogical skeletons with a bunch of useless bones and mirroring along the XY axes.

The issues you described are a side effect of using the script to import the model from the 6th game. In the original game files, these issues obviously don't exist (why would they be there? the models aren't mirrored in the game). The import script is clearly not fully developed, but I think it's worth thanking its author at least for the fact that it works, even if it's not perfect.
So, regarding the "obstacles" from the developers of the 6th game, it's a rather... debatable statement, but okay, if you say "obstacles," let's say "obstacles"))