There were several defenders he tried to bring in and it was a dead end like the case of Jonathan Tah who ended up staying at Leverkusen even though previously for rumors he would go to Bayern this season there was even news about a personal agreement about it.
In addition, Ito's severe injury also made their defensive line find another complicated situation where hope was in Ito but he still could not be played until now even though they had previously lost De Ligt who was left to go to Manchester United.
Bayern's defense can actually still be stronger but sometimes the situation where Kompany's scheme is always offensive and forces their full-backs to overlap it always backfires where they are not too ready to counterattack, so when there is a slight change or at least the players in their full-backs are not too far raised to maintain midfield stability then their defense can actually still be improved slowly.