If Fouss were a stronger defensive 5, I'd agree. Fouss is strong, but for a D1 big is a pretty average athlete.
Keba's defensive upside as either a 4 or 5 is considerably higher than Fouss's. But regardless of the ceiling of both guys — I expect Keba to be the better defender Day 1. Which is why I think he'll likely open the season as our starting 5.