I feel it a bit harsh to say Tito should be sacked but I do have some serious criticisms. His tactics were incredibly poor against big teams except vs Milan in the 2nd leg and my single biggest problem is that he waits until the last 10 minutes to react.
Quite literally at least like 10 times throughout the season, I watched Barcelona look completely clueless for the first 60 or so minutes and thought "Ok, time to switch things up" but Tito didn't make the subs until after the 80th minute when it barely even matters! I'll use one big example of my problems with him.
Bayern first leg: First of all, Messi shouldn't have started but I'm sure Messi had some influence on that. He should have seen Messi was not at his best and subbed him off at half time and rested him until the 2nd leg. Secondly, he should have started with a double pivot. Song's strength and athleticism would have helped a lot vs an incredibly energetic Bayern that were overrunning Busquets. Song would have provided extra numbers in midfield, height, physicality, and freed up Busquets to play some more intelligent forward passes. Thirdly and lastly, he didn't react until the very end. He should have brought on Villa at halftime or made some sort of change when we were only down 1-0. At that point, the tie was still completely open and even a 3-1 loss would not have been that bad of a result. What did Tito do? He waited until the 83rd minute to make his one substitution of bringing Villa on for Pedro when it was already 4-0. Good managers make changes as soon as they see that something is not working but Tito just waits until it's too late or until Messi saves the day.