Two major areas of difference: mechanics and intangibles.
Mechanically speaking, Allen's release is far superior to Jackson's. Fast, compact, and generates a ton of velocity. Jackson's long wind up delivery and release is just so much slower and those nanoseconds are that much more critical at the NFL level.
In terms of intangibles, Allen's leadership jumps off the charts, both on and off the field. And he's worked his ass off to give himself the shot that he did. I'm not knocking Jackson's effort in that regard, but Allen overcame a lot more to get there, imo.