If you think Garrett's bad, you haven't watched much LSU football.
Garrett gets blamed for results, not the quality of his decisions. The timeout in Arizona, the three and out in New England, and the interceptions against Detroit were questionable decisions, but you're just playing the hindsight game if you call them the worst decisions you've ever seen.
I think the worst decision he made was not calling the timeout after the completion to Dez in Arizona. Really there was not much to lose by calling a timeout and running another play.
He'll do better at game management, I think. He's offloaded some of his responsibility and has a year under his belt.