I don't know what makes you say that. Schaub hasn't proven anything. Look at his career numbers:
Games started: 2 (Both Losses)
Passes Completed: 56 of 119 (47.1%)
Yards: 667
YPA: 5.61
TDs: 4
Ints: 4
Fumbles: 2
Fumbles Lost: 1
QB Rating: 61.9
Sorry, but those are AJ Feeley-like numbers. In fact, his career QB rating is only 0.2 points better than AJ Feeley's QB rating last year. Hell, Feeley has a better career QB rating (67.3), and had a much better career QB rating at the same point in his career (Feeley started 5 games his second season, and posted a QB rating of 75.4).
There's absolutely no reason to believe that Matt Schaub is anything more than a backup QB.
Yes, LT is probably the best RB in the league, but a great RB doesn't ensure great play at the QB position with just anybody. Just look at our Phins if you want proof of that.