I think the trade offer talk is a bit much. I would think that after trying and failing to win a starting job on numerous occasions, teams would look at his body of work this year (1 quarter and change) in Seattle and say to themselves "so what, it's Seattle." I don't think garbage time vs. Jacksonville is going to weigh more heavily than...the rest of his entire career.
It is true that he wasn't a disaster as a starter here despite having far less of a team behind him, but there's a reason he wasn't viewed as the answer in Minny, Seattle, or Buffalo. No matter how loaded or how crappy a team he was on, no coach was able to talk themselves into staying with the guy. And teams with really bad QBs aren't looking for the career journeyman, they'll roll the dice with a young unproven draft pick or backup (who may end up being worse than TJack, but at least you don't know what the ceiling is yet).
I think it's a perfect fit here, for the team and for him.