What developement willl she get leading a book. She can easily be on a team and have her own motivations and her own mission statement and that being a primary reason why she doesn't want to lead a team of X-men. If Storm is leading a team of X-men it's because she is fighting for mutant rights. Been there, done that, still doing it, and don't need to be a leader to get it done. As leader she is worrying about keeping the team together, keeping the team focus, staying in control for the team. Whereas with not leading for all we know she could be the baddest bitch where everyone like "WTF this Storm been?" Come on girl we need to dial this back a notch, please." The fact of the matter is we don't know what we don't know. But this is the most promotion Storm has gotten from marvel in a long time and it's across mediums.
100% agree on a solo book but there's no way to know that isn't happening. This is phase 1. We don't even know the staus quo yet. For all we know they could be going around spreading the word of Storm from coast to coast and building her up as a goddess. We just don't know yet.