I don’t have a problem with Ellen Paige as Kitty Pryde. She did just fine as Kitty. My problem is how she was used.

Modern Kitty Pryde

Kitty has the power to phase through solid objects.  The movies tended to use her power defensively only. Properly harnessed she could be an ill fighter.

Case in point Astonishing X-men #7 Kitty hides on the other side of a wall where her victim unsuspectingly stares in the mirror. Before Emma can react Kitty has given her the business.