One of the most common complaints I've seen about Precure is that the leader is always the pink one.
While a change of scenery is always nice, I have no issue with this, as they for the most part stand out on their own. People thought Megumi would be a Mana clone, but she quickly proved them wrong.
In Sailor Moon we have the protagonist who's theme is... yellow? But her costume is blue?? I guess cause the moon is represented as yellow, but then we have Sailor Venus who has largely the exact same color scheme??? I mean I get that she's supposed to be the decoy princess but arranging the five of them side-by-side looks kind of weird.
So why not have the green cure be the lead? I think one word has everything to do with it. Heart.
Hearts are pink and Precure is all about love and friendship and all that other girly stuff usually resented by the color pink. The leader of the team is also usually the heart of the team. She's the one who keeps everyone together. She's the one who most learns and grows from her experiences.
She's the one who has the most traits the target audience relates to, whether it's being insecure (Tsubomi), unable to decide your direction in life (Nozomi) or being clumsy and silly (Miyuki).
For a show like Precure, it's hard for me to imagine the leader being anything other than the Pink Cure, especially when thinking about the show itself immediately fills my mind with loads of pink.