I watched a video with Alex Hirsch and real life twin sister talking about how they were the inspiration for the Pines twins. And so Alex is Dipper and probably focus on him a bit more than Mabel. In the interview they talked about one of those times where Dipper gave up something for her, and he said something to the extent of Dipper needed to learn something here and be the bigger person. But I don't think he put as much emphasis on character growth for Mabel