Your points are actually conflicting. Tubby moved Blake to PG to play his 5 best players and it didn't work out. The basketball reference doesn't have anything to do with this Shortell situation and if you wanted to make an analogy, it would probably be the opposite.
However, to your original point. Everyone likes to assume that everything else would have remained as it was if Shortell would have started. So, lets assume that and assume Gray was at WR. What happens when Shortell goes out with cramps...Tom Parish? You don't really expect Gray to take snaps and practice as a WR/QB?
The fact is in football is that you NEED depth. I like having two QBs that can play a bit. Shortell was impressive, i'll even give you that he was slightly more impressive than Gray. However, it is is an extremely limited sample size and it could only be argued that he was marginally more impressive than Gray.
You need to be pragmatic about these kinds of things. If we notice this trend continuing in week 4 or 5, we might have something to talk about. But then you'd still need to address the depth issues. After Shortell has 1 impressive drive and almost identical stats to Gray, lets not get carried away.