Anyone who says differently (including a belief that JL was the second coming of Joe Montana earlier this year) has missed the last four years.
In 2008 JL sucked, but there are a lot of good QB's that sucked their freshman year. In 2009 we didn't see enough of JL to really tell. In 2010 he definitely had his moments. In 2011 he was playing like a great QB... until JJ showed back up. I suspect that JL had a hard time in those circumstances as he had to have confidence issues when Miles was favoring a QB that was evidently not very good. It's not likely that he'll become an NFL caliber QB, but it isn't an impossibility.
I suggest you look up Elway's first 3 years in the NFL. You would have been saying the same about him. I'm not saying JL is Elway. I'm saying he deserves his shot. Many others agree.