I think he means that you would ideally want the best German talent to stay in the German League.
It's similar to how the English pundits were sneery towards the Kane to Bayern transfer coz they want Kane to stay in the PL.
It's definitely better for competition within the league. It would be even better for the German League if Wirtz stayed at Leverkusen but that won't match his ambition.
Can't remember many wanting Kane to stay in EPL most of the voices I heard wanted him to leave and was happy he choose to do so instead of going to a direct rival of spurs for the CL.
The only thing I heard was about him being all time EPL Scorer.
But he and spurs did the right thing, because it's lame to just move to City after leaving spurs if you're Kane.
The narrative these days is it's a good thing English players are starting to move outside England.
I understand the wanting best players for X nationality to stay in there domestic league,but that's not what Bayern is doing/does.
They are just on some lame shit, them and the entire league that happily goes along with it.