You don't need a whole lot of 3s from high usage players. A low usage guy that makes 150+ 3pm is still going to give you 200 3pm in a full season. But 3s are very important... you just don't have to get them all from a high usage guy.
If you want to keep the basic usage structure you have going, look for a guy 55%+ efg% with around the same combined rebound percentage (but higher defensive boards) and who fouls less. I usually go for a tier 4 usage or lower center and get most of my usage from 2 positions (generally SG and PF). I generally like having 12.5 to 14.5 usage points in my SL. If you don't understand what I'm talking about,
read this thread.