Our 'big' lineup with Morgan-Kiah-Stewie across the back has easily been our best defensive lineup this year against the better teams, by a lot. As in night and day, game-turns-around kind of difference, in several cases. Also, we have this year still been able to generate transition scoring with the big lineup.
We can go with KML or, in certain situations, Nurse alongside Moriah, but regardless, the substitution of Kiah in the middle has negated much of the advantage that other teams might have with quick, penetrating guards. The big lineup has been lights out on the defensive end.
If the half court offense flowed as well with Kiah in the 'big' lineup as it did with the usual starting lineup, Geno would use it more often, but it doesn't and Kiah is not a consistent scoring threat, so he doesn't.