re: What are the five worst P5 coaching jobs?

The criteria of best and worse is in the eye of the beholder.

Winning a national championship. These are all good candidates.

But keeping a good job long term depends upon a teams historic potential and fan/administration expectations and tolerance.

For example Texas, medium low to medium high potential, very high expectations, and low tolerance would be worse than Vandy.

Unasked, but the best P5 job for championship purposes for new or current coaches are LSU, USC, and Tennessee.

LSU very high potential (2nd most Nattys in the BCS/CFP era and 3 different coaches obtained the goal here) matches the very high expectations and low to moderate low tolerance. Both Southern Cal and Tennessee have high historical potential, and the expectations and tolerance factors have been beaten into submission by current failures.