Well, there are a few things you can try. I would (specially on the fast trainer) try to add the points to the skill column that you expect them to do better with. On my team this means Physical Mental. My midfielders gotta be strong and speedy.

I expect you have tried them in all the positions and they still perform bad? Some do like center, some right or left.

Have you tried arrows on them? I also sometimes play them OOP.

If you can play a friendly or a few it can help you figure out where they like.

If you haven't had them very long, I would give it some time. I usually give my guys a "bye" on the ratings their first Season, as I play them and program their numbers they get better, but keep in mind too, MC's are notorious for bad ratings in this game.