I feel like THE biggest question to answer is this:
Given a 4-person base team of Biles, Jones, Lee, and Carey, who can regularly beat the top 3 on each apparatus listed below?
VT Simone, Jade, Shilese
UB Shilese, Suni*, Simone
BB Suni, Simone, Shilese
FX Simone, Shilese, Jade
I honestly don't see anyone doing it at this point. So it makes more sense to take an AAer as the 5th person. Jordan fits that.
*I know we haven't seen Suni's bars yet, but she's a multi-medalist, and she's capable of an "easy" routine that is still better than everyone else's except Shi's. Probably better than a theoretical Douglas, too.