A lot of people can take credit for new mutant poppping up. It was a group effort.
Hope obviously did the deed. Stark figured out what needed to happen. Iron Fist and Spider-Man helped train her. And Wanda in the end helped Hope release the Phoenx, which repowered the mutants. And yes, Scott championed the idea at the start. In the end everyone wanted the same thing and got what they wanted, so it all worked out for the best.