Before the Patriots gave him a tryout everyone was talking about how he'd worked with former pro quarterbacks and his passing was much improved and his footwork had improved and all the rest. It took Belichick about 5 or 6 weeks to determine that nothing was different.
Belickick also chose Bledsoe over Brady. Brady was 3rd string his first year, as I recall. Then, Bledsoe got injured. What Brady brought to the team was something you don’t see until a few games are played, and it comes down to the wire: heart. Tebow had heart, too, and managed to win a lot of games when he was given the chance. I think the biggest obstacle for Tebow is that a team has to change its offensive scheme so much for him to be successful, and then, if he ever got injured, the team would be screwed. Better to stick with standard issue quarterbacks for most teams.