If we had an experienced QB who could move the ball and not have turnovers, he'd be playing already. We don't. It's a big reason we're having to throw a true freshman to the wolves early.
And despite his mistakes, Sims is a lot closer to where we need our QB to be this year than Graham was last year, and the quarter or so Graham got against BC doesn't really make me think he's addressed the issues he had last year. Sims has issues with turnovers, but largely that is issues on a small number of plays, and while those have big consequences, it's easier to solve an issue that affects 3 or 4 plays a game than one that affects 30+.
Sims had basically 8 drives against BC (not counting the drive starting at the 17 with 26 seconds left). He led us to 3 TDs, for a ppd of 2.675 which is a very respectable number and a significant increase from last year. That is with another drive that probably should have ended with 3 if not for us having no kicker. A FG there would have put us at 3 ppd which is certainly a good mark.
To compare, Graham came in, had 4 drives, 1 TD, a 3 and out, a 4 and out, and a solid drive ending in FG range, that started on their side of the field after an onside. His ppd was 1.75 (giving him the extra point because that missed point had nothing to do with Graham at all). If we make his FG then he's sitting at 2.5 ppd.
The truth is Sims moves the ball and produces more than Graham did last year by a good bit, and likely more than our other QBs. It's why he is playing. What we as a team is what Sims gives us AND for the TOs to be cut out. When we did that we put up nearly 4 ppd. It doesn't do much good to make the change to cut the TOs at the expense of the playmaking and ability to sustain drives. That would make more sense if we had a good defense which lends more value to the field position that comes with punting instead of turning it over. But we don't have a good defense so the relative value of a punt vs a turnover isn't as high. And before people say that he isn't improving or learning from his mistakes, he threw 8 Ints in his first 3 games, and while not all were entirely on him, a good many were. He's cut that to 2 in the last 3 games. So there is improvement on the INT front. He has to address the fumble issues but part of that dynamic is getting a center that is more consistent with snaps as two of the fumbles he's had recently have been snap related.