There are lots of important games waiting for Leverkusen after the small break. Every time we have these breaks I hope that it doesn't do any harm to a team like Leverkusen as they are in such a great condition. They are playing against Dortmund and Stuttgart before the winter break and I hope they don't fail in those games. I wouldn't mind if it's Dortmund or Stuttgart to compete with Bayern, but from all those teams Leverkusen is really by far looking to be the strongest and most consistent. Dortmund is weird. They get celebrated one week just to play bullshit the next week.
Of course Xabi will use the international break as best as possible to analyze their future matches and fix the shortcomings in his squad. I hope they will continue to provide competition against Bayern Munchen this season, because we know Dortmund is unlikely to be expected to do so.
Dortmund and VfB are the real tests for Laverkusen after most importantly Bayern, but we have seen that Xabi squad was able to hold Munchen to a draw at the Allianz Arena previously, so I think Laverkusen will be able to overcome both of them later.
In the end Dortmund had to give up third place in the Bundesliga standings for VfB, their performance was very far from last season. I really didn't think that they would have to lose to VfB before, and on the other hand Tuchel squad must be fully alert if they don't want to lose their dominance this season.
These breaks usually interfere more with strong phases that teams like Leverkusen is currently having. These breaks are either good when a team is not doing very well or when it means some more time to recover for players who actually get a break. But most of the players are also on tour with their national teams and don't usually get additional breaks.
The game that Dortmund lost against Stuttgart was not only a bad result, but also a lesson that Dortmund should stop underestimating any team from the Bundesliga. They had only one shot on target in the game. Stuttgart had 22:5 attacks and 10:1 shots on target... You would think that Stuttgart played against some team from the 2. Bundesliga.