Crazy that there's 55 pages of arguments on this. Panthers gave up a 5th and a very below-market salary for a guy who has had two QBR ratings above 50 (average starter), one above 60 (very good), and one of ~35 (quite poor, but he was playing hurt).
It's only a 'bad' trade if you think he takes the Panthers into NFL purgatory (not good enough to make the playoffs, not bad enough to draft his replacement). But from a pure W/L perspective, it's a boon.