Shang-Chi store coming

Having him MUCH higher changes the way you play him and makes him a viable option vs the other fastest characters. 

Once he's at a high enough level you can basically just match red/purple every turn and smash faces, without having to combo off at all unless you feel like it.  That playstyle really doesn't kick in until you can get him extremely high level though. 

If you're trying to allocate resources optimally, putting more levels on power booster characters will always be optimal because it effectively levels up your entire roster at once.