Steals are more likely to lead to runouts, so I'm going to put more weight on those. Plus, they're easier to look up.
True, but you also have to think about the nature of our steals. Often we think of steals as a defender stealing the ball from the ballhandler, and we don't do that a lot, nor does Frank emphasize that. If you think about what our defense does, one of the primary things we do well is making the balhandler uncomfortable and forcing him to make passes 25-30 feet away from the basket. Therefore when we do get steals, most often they are stolen passes (usually bad passes), just like the TOs we force are mostly bad passes, often just thrown out of bounds to no one. So even as a measure of perimeter defense, steals can be deceptive in Frank's defense because the steal usually comes from a defender off the ball that is defending a pass reciever and not usually just taking the ball from the ballhandler.
Also, this sounds like a great _FANalysis basketball breakdown; going back to look at good defensive games (like Tech) and breaking down the numerous TOs/steals and how we forced them.