It’s good that you brought up Alex Smith. But you didn’t pay attention to what really happened. The “plan” Harbaugh clearly had for Smith was to keep him in there long enough to train his replacement. He drafted Kaepernick, had him go through camp, put him in a couple of games, and when Smith got hurt put him in permanently, Smith came back from injury to the bench. And now they jettisoned him and KC, a team that’s DESPERATE for a QB picked him up. He never flourished, he survived until his replacement was trained.
Tebow has had plenty of chances. His stats stink. And there was practice time. If he was impressing on the practice field he’d be starting, he didn’t, so he didn’t.
As for Smith, he was given a system- and a chance- to succeed. He proved he could win. SF just got a better deal out of it with an heir, not unlike Young/Montana. Imagine where Alex Smith would be today if teams had listened to the alleged 'experts' 4 years ago... he'd be holding a clip board, or worse.
As for plenty of chances, how many full seasons has Tebow started for a team? I'll wait...