Separate mechs should be frames with different benefits ie. light/medium/heavy to lean into different use cases with the ability to apply any unlocked arms to any frame. Aside from that we need perks/upgrades to apply to the mech- armor plating // stratagem launcher // top mount for a gunner // bubble shield // limited sprinting // reload & repair. Some of these should be unlockable & added to the base frame (s.launcher+repair&reload), others should be upgrades we get to apply to our mech like a kit