For all we know, the Jets could have given Tebow a legitimate shot to beat Sanchez, but he was terrible in practice and therefore never saw the field.
And the reason why Tebow was the game-day backup is quite simple: with only 46 roster spots available, it made more sense to keep Tebow active (to play multiple positions -- wildcat, punt protection, etc.) instead of McElroy (who only plays one position).
You're making sense. Ultimately that won't matter to Tebow fans though. Suppose Tebow started week 17, even though coaches thought he shouldn't. Suppose he turned the ball over 3,4,5 times, played terribly and go booed. Tebow fans would just be saying he didn't get enough of the chance, that he DESERVED more of a chance, that he DESERVED to compete for the starting job next year. His bad play has constantly been ignored by his fans. Look at his last 5 starts for the Broncos and you see 4 bad performances, but you wouldn't know that happened according to Tebow fans constantly saying he won a playoff game. The same Tebow fans that ignore the playoff games that Sanchez has won.
Sanchez is bad. If Tebow's not starting it's for the same reason other players don't start --- their coaches don't think they're good enough to.
The argument that the Jets kept their best QB on the bench because they didn't want his fans excited about him winning a game, if he won a game, is utterly silly. Arguing that Tebow fans are a burden doesn't make Tebow good.