He won one playoff game, and it was his second season.
I rarely saw Tebow play and I can't comment on the oft-heard cliche "Mechanics" that everyone throws around now.
All I know is that most QB's in the league haven't even achieved what Tebow has achieved. The Bills, for example, have been through a string of dull, mediocre QB's over the last 10 years, who were all given 2-3 years to succeed or fail. Same for many other mediocre teams such as Cleveland, KC, Oakland, etc...
As such, without a doubt Tebow is being held to a much higher standard, I suspect because of the PR risk any GM has by giving Tebow a shot.