Works both ways. He could be .911 Holtby or he could be .920 Holtby. Hell, he could be better than what we've seen from him.
But if he's .911 Holtby, he's a backup. Halak is a proven #1, which Holtby is not. At least not yet.
Is a proven 7/10 better than a guy who has a 50/50 shot at being either a 5/10 or an 8.5/10? I don't know. For me personally, I'll always take the experience in net.
If you're ignoring stats and going by the eye test then why use stats like above? Why not admit that both goalies have made great saves and have let in softies (which both have admitted) and really aren't the difference for this team?
Should Theodore have been a backup with his .911 save% in 09-10? What about Hiller, Howard, Anderson, Pavelec and others this year?
You realize that Holtby's career save %, even with the bad games earlier this year, is .917 which is pretty good and solid starter material in the NHL and is THE SAME AS HALAK'S CAREER SAVE %? And Holtby's career playoff save % in 21 games is .931, compared to .923 for Halak in 23 games? Is that an experience advantage or not?
Again, I'm not trying to say one guy is clearly better than the other. I don't think it matters, and to me both are a hair better than Neuvirth. But if we're going to try and use stats to put one guy above the other then let's consider some evidence for both sides and dump the confirmation bias favoritism.
The next time one of these guys lets a goal in, pretend it's the other guy and analyze what your reaction would have been. Then do it on the next goal. And the next. And keep going.