I think focusing too hard on the monster-vs-mecha foundation is unwise, yes.

Ultimately you have to figure out how to make the interplay between the politics of the city defense forces and the pilots interesting as well as non-redundant. It’s kind of odd to say this, but I believe at the heart of any good mecha RP is making sure the pilots have enough interaction opportunities and interesting scenarios outside of the giant robot. Some players don’t agree. I’ve had one player leave because the RP was “too boring” and “focused on too much talking rather than fighting”. It really depends what you are attracting in your playerbase and what they want. Broken Promise had a point to, I don’t know, talk to your people and see how to shape things from there if you don’t have everything figured out from the onset.