I was right with you until the end part including "before him." Even with his great size and good athleticism, I don't think that Thabeet was better/more impactful defensively than Emeka. I guess this could be argued if you focused on the overall threat of the block in the paint, then Thabeet had more of that. Thabeet was smart and learned quickly, looking back on it. He was an amazing find. But Emeka was the emotional leader of the team who was a great defender and rebounder. He became the "Go To" player in the comeback against Dook and just was such a great athlete in his way. The block with the left hand after going to block with the right against Villanova (who did he block?), one of the greatest blocks at a totally critical time in a game!!!
Anyway, I vote Emeka the Greatest UConn (Calhoun onward): interior player, center, defensive interior player, offensive center (junior year), smartest BBIQ interior player (can't count Nadav an interior player here, btw).