A couple of plays here and there in the playoffs is the difference between a playoff loss and a run to the Superbowl. Tannehill has given the Titans a chance every year he's been here.
Sure, he's had some bad games in the playoffs...but so has Manning, Brady, Mahomes, (insert your favorite QB) etc etc. That's part of it. Gotta keep getting there and hope to make a run. That's how it works for every team.
With Willis, it's a complete reset and pray that he somehow miraculously becomes an NFL QB when he looks like he couldn't make it on the local peewee flag football squad. Same with a rookie QB.
What the Titans need most right now is a competent OC. Even with the lack of big name talent on offense it shouldn't be THIS bad.