[@FunnyGuy] Also with the powers growing/not growing thing think of it this way. Technically, for the X-Men their powers don't actually grow. They have full access to them the moment they get them. It's their skill and ability to use said power that grows.

Take Kwan and her power for instance. (If you've seen the Flash tv show then skip the explanation) It is just like a normal runner. They get faster and faster the more they train. Their bodies have the physical capabilities to run at a certain speed from the get go(couldn't think of something better to say there). They just have to practice and practice to make themselves go as fast as they can go. With Kwan her body has the capabilities of a certain level of speed. She may not be able to hit them at first but that is due to her not training her body to accept the speed she can go. She still has the full force of her speed, but it is her skill that holds her back.