[Sombre]

I think your making a fairly big assumption, that mods which are marked 'balanced for vanilla' are actually made to 'fit in' with the vanilla nations. One of the big draws of modding is that you can do something different, not just make a version of Mictlan with different graphics, or renamed Ulm units. Taking Avernum as an example, it doesn't really 'fit' with vanilla nations; it's very different in a number of ways. I never actually made any attempt to make it similar to the vanilla sides.

What I did /try/ to do was make it so you could play it alongside the vanillas and not be hugely over or underpowered. Any constructive feedback helping me do that is appreciated.

I gave you two random examples of how mods can be balanced differently. These methods may not appear in the vanilla game, but when you're dealing with mods you have to accept they aren't always going to follow 'patterns' set out by vanilla. The thing to aim for is to stop them being hugely over or underpowered (worse than the worst dom3 nation or better than the best).