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

Okay. Maybe, for example, make it so that building a super-base requires two regular bases? Or is such a strict requirement unnecessary, and would it be better to simply increase the required town level?

Added 3 minutes later
And here's another idea, can we make a building that only improves a specific creature?

This weirdo proudly bears the name "Two-Faced." His mother conceived with a monster of another race, and the Orcs raised him as their own, and he became a mighty warrior of level 5-6.