Burnley is mediocre team but still, Vincent Kompany manage to guide then to become one of the fiercest mediocre EPL team, promoted them to English Premier League, but somehow they got demoted because they failed to meet the requirements. Perhaps Vincent Kompany found favour in the eyes of Bundesliga giant, he have more work to exercise in his new club, definitely going to be tough for him in the first season because there's more handling responsibilities to take of. The players in Bayern Munich are no mediocre players but experienced players that knows every corner to win games.
Calling Burnley a mediocre team sounds trivial to me, I don't really see them as such, it will be much better and fair if they could be perceived as an average team, anyways that's your opinion and I wouldn't dispute it, after all we are all entitled to our opinion as no one has the 100% monopoly of knowledge and ideas. In the premier league the competition sometimes may make a team seem to appear less of their abilities.
All through the times Kompany was in charge, Burnley didn't perform so badly though they weren't of a very brilliant form but they weren't such that I will consider as a very poor team because the sanction on them also had a way of affected their total performance for the season, before that they were really making good progress amongst their premier league equals, just maybe this could be the potential the bundesliga giant saw in kompany and decided to hire him, because understanding the dynamics of premier league, you will see that it was a huge task for kompany to keep Burnley in the premier league even with all the challenges he faced.
If Burnley was on a clear stands, having not defaulted in any way, it's possibly they would have done much better. The bundesliga isn't an easy league as well and handling a big team in the bundesliga is such a huge one and aswell an honor too aswell and I'm trusting Kompany to deploy all he's got from his experience to the best of his knowledge so he makes his appointment worth the while but then it may not turn out really beautiful in the first days.