Not all bigs are created equal, obviously.
Outside of Serah Williams and Sarah Strong, let's look:
1. Mamel and Quinonez are freshmen international players
2. El Alfy has been inconsistent all season, but admittedly has had some good moments
3. Brady has largely been a bust
4. Patterson and Ducharme have largely not played at all for 2+ years due to injuries
Before Williams signed, Strong was the only consistent inside force for UConn, and she's still only 6'2. They needed an upgrade from El Alfy, and got it in Williams. That lets El Alfy slide over to the bench and probably lets her play more aggressive defense since there's less of a drop off if she gets in foul trouble and they have to rely on an unproven freshman.