in my opinion it might be possible that soi fon might fight halibel first, and loose. With soi fon being badly injured unohana comes in and takes over, kind of like how zaraki bailed ichigo out.
if you think about it that way it would make some sense. with three of the espada remaining (if/when noi dies and ulquorria likely reserved for ichigo). otherwise, it would be kind of unrealistic for us to see every captain fight to their true potentials unless bleach isnt ending after the WW.