I honestly think Kovac is not a bad manager. But he made a few mistakes that cost him dearly. Saw a Tactical analysis after flick took over where it showed that he played with a larger gap between players that made passing riskier and was prone to those dreadful counterattacks (flick seems to have seen that and shortened it a bit, making the defensive midfield much more stable). For the rest, i think that the team did not play that differently for a while but it felt much better right away. And obviously he was unable to bring everyone on board, shaking the hierarchy in a rough way (it was really not a good move to humiliate muller in public before he was over). There were a few other tactical probs i guess and the lack of support from Rumenigge did not help of course. It’s often small things or one or two players’ performance that can change a lot