Not true you do not have to make Steve and Tony save the mutants no one else want this would make the X-men obsolete and the opposite is also true if the X-men saved the Avengers in each event.
What you need to do is show the readers that although they can not do much to help mutants they care through small gestures and support.
For example if Cap had told Scott that he would go public against the cure it would not stop the government but would prove that Cap cares and will help the mutants as much as possible for him.