RTF is a global modification that replaces all towns in the game.

It's an interesting idea, but I doubt it's feasible. That is, creatures in a squad receive some kind of bonus, similar to master artifacts?

similar to the 8th levels in WoG. We get creatures that are significantly better than their predecessors (within reason), but at a high cost. Let's say a level 25 hero, with a mastery amulet and all the abilities, could upgrade 100-150 creatures, but these would be such good creatures that the player would sit and think whether it's worth upgrading to tier 7 or stopping at tier 6. It would also be nice if they were upgraded depending on the tier, that is, tier 7 - no more than 5, tier 6 - no more than 10, etc., but I guess that's impossible.

Added 2 minutes later
This idea won't limit the mod's authors in terms of units, there won't be a change in gender during upgrades, people won't turn into animals, etc., but at the same time, you can take any city and replace the people with something else