There'd quite falling elite teams that's struggling to buckled up. Harry Kane might be the major reason why Bayern Munich have failed to win the Bundesliga title this season after winning it close to decades in rows. It's questionable because Harry Kane have never lifted a major title with the club's he played for and therefore leading to what we called "The Harry Kane Curse" the exact same way we have the "The Drake Curse" when it comes to betting. Football is never as we assumed it to be.
I don't believe in superstition or anything like Harry Kane curse that so far they have never won a single prestigious trophy, making Bayern Munich fail to win the title which they have always won in the last 11 years. Bayern Munich failure to maintain their dominance was because they failed to match Leverkusen level. Leverkusen's might was the reason Munich lost the Bundesliga title.
If this assumption is correct, the failure of the English national team in various major competitions is due to Harry Kane curse. If at the start of the season he had moved to Real Madrid, would it be possible that Real Madrid would have bad luck this season like Bayern Munich experienced.?
This is something that is still very debatable, because a curse cannot be proven in any way. As you said, Bayern Munich's failure was because they couldn't match the performance shown by Leverkusen this season, so they couldn't defend the championship title they had dominated for seasons.
Harry Kane is still very good, he is even the top scorer now, is it possible that a player who scores that many goals is the cause of Bayern Munich's failure? I think that is unacceptable by common sense.
This was just bad luck, because when he moved to Bayern Munich there was a team that could show something extraordinary like Leverkusen. so that made him fail to get a trophy again in his career.