I don't agree with your assessment but I will just say this as far as your 1 and done deal:
RG3, top 10 in NFL stats running the spread option.
Colin Kaepernic, top 10 in NFL stats running the spread option. Replaced a very efficient WCO game manager and pocket passer.
Russel Wilson, top 10 in the NFL stats running the spread option. Usurped a pocket passer with a huge contract.
Cam Newton, moderate success running the spread option.
3 out of 4 are in the top 10 in the NFL.
3 out of 4 of those teams are going to the playoffs.
Out of those guys only 2 have NFL caliber accuracy and releases. Wilson and Cam don't. I don't believe that Cam Newton or Russel Wilson is any better at reading defenses than Tebow.
It's one thing for Cassel to go from our system to someone else's, but the spread option has proved successful for a lot of different style quarterbacks and Tebow is one of the best at running a spread option.
I want to see him running an NFL level spread option, like all those other quarterbacks, before I will agree he's no good at this level. Those other guys are getting their amazing completion % that are rivaling our HOF quarterbacks due to the spread option offense, not because they are that damn accurate. The scheming just makes it so much easier to complete passes.
Here I will just quote what Urban Meyer said recently:
"I don't get to watch much pro football during the season, but my offensive staff at Ohio State put together cutups of all these NFL quarterbacks: Cam Newton, the 49ers quarterback [Kaepernick], Russell Wilson and RG III [Robert Griffin III]. We watched four hours of film. That is the spread offense. It's not just a version of it. Tim is a spread offensive quarterback. He can run the spread as well as anybody in college football history. The only question is whether you can do it on a consistent level in the NFL. No one has been able to do that yet. But there are teams out there now running it. I had no idea until I saw all that film."
The issue isn't that Tim Tebow can't run an NFL offense or that he inaccurate or has issues with his mechanics. It's that the coaching staff he has worked with either refused or didn't develop the spread option offense for him. Everyone keeps trying to make him do something else, while all these other kids are getting praised for the fact their teams have bet the farms on the spread option and making it very easy on them to transition to the NFL.
Why shouldn't Tebow get this same opportunity if it is proving you can cut through NFL defenses like a hot knife through butter with it and make the playoffs with freaking rookies? He already did the same in a makeshift version of it in Denver, created by a staff in one bye week, that didn't really believe in it, who have primarily ran old school NFL offenses, and mainly relied primarily on the read option, rushing aspects of it.
I think he's earned a chance too. And there are far too many BAD NFL offenses with BAD pro style quarterbacks for someone not to give this a shot when it's clearly working. Even if it's for 1 year to the playoffs, it's still worth it.