How do I balance game interactions between a giant mecha that can level cities and its pilot?


I have had recurring trouble with a subject I like, and would like to implement into my games, but can’t find a good way to do so: mechas (big huge robots)

From a system point of view, it is usually quite easy: just a big suit of armor with specific weapons. The pilot has to be inside to be able to use it, and it is too big to use just anywhere. Most systems can allow it.

However, I can’t find a good game balance for it. The main problem is that the whole “normal person when outside the suit / super-destruction-machine when inside the suit” makes too much of a difference in-game. For example, any challenge when the pilot is outside the suit is a trifle when in the suit; while any challenge for the suit is impossible for the pilot. It ends up feeling like playing two games at the same time: the mechas’ game, and the pilots’ game.

I have tried reducing the difference between the pilot and suits (making the pilots stronger and/or the suits weaker), but then the suits have almost no use, and the players end up almost never using them.

I have tried mainly in BESM (since it is already implemented), D&D, and even tried to develop my own system (with Mecha/pilot classes and perks). I’m looking for a Gundam/Front Mission style, i.e. mechas are big and powerful, can potentially be destroyed by well-equipped and organized infantry, but are mainly in their own world (mecha vs mecha)

So the question is: how would you balance a game focused on mechas?