I've tried to remain agnostic in the QB debate, but the limitations that Rees places on the offense are too much to ignore, which is why I lean towards hoping somebody else can win the position. I do believe that we could have a good to very good season with him as our starter (no, the world won't end despite the histrionics of some). However, his physical limitations hold back the offense in ways that seem pretty fundamental to the offense that Kelly wants to run, namely the threat of the QB run and the vertical passing game.
Yes, we lost production after Jonas went down last year, but he isn't coming back and I, for one, am not sure if Riddick can fill those shoes yet. The other problem, as I alluded to above, is that with Tommy's limitations opposing defenses don't have to be too concerned with him keeping the ball or throwing it over their heads. The running options are more limited and the defense can keep more men closer to the line without too much fear of having the ball get thrown over their heads.
Lastly, while it's great that Rees is smart enough to handle checks at the line, near the end of the year it seemed that teams had figured him out and were showing him looks to bait him into a check and then backing out of it at the last minute.
I admire your rational approach and optimism. I don't think our views differ too much either. I'm just a bit more pessimistic on Rees. I just fear that if he's named starter our offense's ceiling would go from potentially explosive to potentially good.