Good players do not guarantee that they will qualify from the group stage, or even become champions, it's true. Because the performance of players always changes every time, physical factors and strategies that cannot be executed well during the match on the field have a significant influence on the final result. There are many histories of good teams in the domestic league failing in the UCL, this is enough to be part of the facts that cannot be avoided. Although Bayern performed well so far and maybe become favorites, I hope there is a team that is beyond expectations that can reach the final like last season, when the quarter-finals to the semifinals were unpredictable results.
Exactly, many reasons can be the basis of a team's failure to be able to compete for trophies, even though it is a big club that has a long and glorious history in previous years. If you look from the other side, i actually think a coach who decides to join a big club will have a heavier burden, because the fans will raise very high expectations of the coach to be able to bring their favorite club to become champions, not only that, to be able to adapt to the players is not an easy thing, to get a suitable strategy requires patience and strong leadership.