Okay, before I look into anything else, I want to say that not everyone should have flight.

This is mostly for balance. If only a couple people can't fly, it's difficult to include them in combat while keeping threats applicable to both land-based and ground-based players.

If you want your mecha to fly, they should probably be lightly-armed and armored and specifically designed for flight.

That said, boost jets and jump jets are perfectly fine, they're not flight.