Bundesliga title was won by Bayer Leverkusen because Bayern Munich wad not in form previous season. The Bavarians are here to stationed winning and we know it's up and running. Bayern Munich new coach will do better, I know this actual fact for sure. Vincent Kompany is classified mediocre because Bayern Munich happens to be the first top flight club to manage as coach and we know what's capable of, he will put in enough work for the purpose to succeed in his first season.
Been speculative with this which you have stated is good but I wouldn't want to consider t whole enough because if you look at the structure of Bayern Munich currently, in as much as they would want to regain back their dominance and take over the bundesliga once again, they don't have a very stable or strong structure currently and all of these are needed if they will be able to take back the league because away from Leverkusen is other teams too who are trying and hoping to attempt the league title and they are not promising an easy league struggle in the coming season, so Bayern Munich needs more than just the speculations to get back their face in the bundesliga
Talking about mediocre coaches, I don't think kompany is or should be seen as one, he didn't get to do excellently with his former team but still he isn't a mediocre and optimistically he may do better in Munich especially with the fact that all that he will be needing will be very much available aswell as he's got a team with a good depth so the Job isn't supposed to be a really hectic one but where he may need to put in the work will be with his technicalities after which the rest may just be on auto pilot (lol) considering the kind of team Bayern Munich is in the bundesliga and they still have their depth maintained.