I think Rogue easily receives more development in X-Men than any of the younger mutants in First Class. Actually, I think Rogue receives more development in X-Men than most characters see throughout all 5 films. She has a clear beginning, middle, and end with regards to what her life is like before her mutation, after its onset, and after she is taken in at Xavier's school.
That said, I like what I saw of Banshee and Havok. I think Caleb Landry Jones and Lucas Till are great in their roles and provide both of their characters with pretty distinct personalities. You also make a good point about each undergoing their own change, even though it may be small. Banshee does spread his wings and Havok does become less of a jackass.