My 2 cents:
It feels kind of awkward that additional propulsion slots slow you down on the ground. I mean, I kind of get it, but in practice it means weird situations like when you go from 70/40 weight, equip a third treads, end up at 70/60 weight and are slower than when you started. Slots are a pretty huge investment - if your return on that is at best a tenth of a move per turn and at worst a handicap you're going to probably go for utilities instead.
In general speed calculation feels weird on the flight end, too. The marginal benefits of 1/2/3 imp flight units are 3.333 moves per turn (base), then 1.666 moves, and finally a full 5 moves per turn. Maybe it would be better if there just was a base "speed value" and "speed bonus value," and applied the slowest speed value first, then the rest as bonuses? For flight units this would probably mean more modules needing to be equipped for the mythical 10 delay shit, but possibly also 10 delay being more achievable without the 3x prototype build. It would also mean that you could be allowed to stack as many flight units as you wanted, because you wouldn't hit a "0 move delay" point where the game breaks. I have no idea if this would overall work out, but it feels like it would be easier to understand than the current calculations.
Also: wheels seem really worthless, but I can't really tell because there are so few wheels in the game. In general, though, their durability seems far too low to justify them (even on -10), and I think you are literally better off with 1x overweighted hover units than wheels, in almost every possible way. At the very least, I think wheels should have a 0 penalty for additional modules, since they're the middle of the road option.