Individually I don't know. Against nearly everyone who played man (other than UConn and Pitt, of course), Billy was able to dominate even as a sophomore. He disappeared sometimes against zones. But most kids learn how to shoot eventually, and his mechanics were fine. A little slow. He'd have benefitted from good teammates through his junior year, and imagine McNamara as only a 30-mpg player in 2006 with Billy playing extended minutes alongside Devendorf. That could've been a great combo.
From the team perspective, I once estimated that Billy in the lineup for all three years would've netted SU at least 16 more wins. Found my notes from back when I had time to conduct these ridiculous hypotheticals (and save notes about them):
"2004: losses to Providence, Notre Dame, and BC become wins. We'd be 24-5 or 25-5 after advancing and losing in the BET and would've earned way better than a 5 seed in the West with UConn. Probably would've played at the Meadowlands and could've squeezed a couple more wins out of the draw.
2005: losses to Pitt, UConn, and BC become wins; even if we split Pitt and UConn (three of those four were close games), we'd have ended up 30-3 and the 1 seed in the East without ever having to see Vermont. Final Four favorite.
2006: losses to Florida, Bucknell, Seton Hall, Cincinnati, DePaul, and Nova become wins. Totally different complexion for a young team, burden would have been taken off the big men and McNamara and team could have developed normally instead of losing early games and having crazy no-shows against Cinci and DePaul."
Lot of what-ifs in there, but these college teams are so often a house of cards. Losing one guy changes a lot.