FSU tanked because of his failure to hold their OL coach accountable for his bad units, lackluster QB development, and lackluster WR development. I don't know enough about FSU back then to explain why he wouldn't fire Trickett, but that's definitely a knock on Jimbo. As a HC, Jimbo's QB starters are as follows: Christian Ponder, EJ Manuel, Jameis, Everett Golson, Sean Maguire, Deondre Francois, James Blackman, Mond, King, and Calzada. The first three operated his offense at a good to great level while the next four generally did not. At A&M, Mond ultimately was fine in that regard while King is unproven and Calzada has definitively failed.
I ultimately think they're on the upswing because Conner Weigman is extremely talented and pretty athletic. In my opinion, their recruiting on defense as well as Henson's development of their OL gives them a 3 loss floor going forward. You and everyone else can argue that Jimbo won't develop Weigman like he didn't develop FSU QBs from '15 onward, but I just think Weigman is a special prospect. As far as WR development goes, he has continued to let some talented guys wither like did at FSU because they're typically asked to run option routes and Craig is a terrible WR coach (but great recruiter). If they continue to get decent to bad QB play along with lackluster WR play, then they'll likely have season after season like this one in which their defense carries them. If my opinion of Weigman rings true and he operates Jimbo's offense anywhere near the level Jameis did, then they will compete for SEC titles.
As far as Jimbo's coaching goes, I think their season turned starting with the Alabama game because he simplified their offense for Calzada by running much more RPO rather than his typical offense. Calzada just isn't a good QB because he can't quickly process reads, so the increased RPO frequency gave him easier throws and thus more completions. If he fails to develop King and/or Weigman, then y'all will be right.