First of all, they lost Robert Lewandowski. Then after that, Choupo Moting seems to be playing quite decently. Even though he was not able to fill the void that was left by Robert Lewandowski, but he was at least trying to do what his team needed him to do. I do not know if Füllkrug will be able to produce what even Choupo Moting was producing. This has been a very sad situation for Bayern Munich. They wanted to improve their attacking capabilities by bringing in a competent player with the money that they got by selling Robert Lewandowski. But that plan absolutely failed.
Bayern remained strong and strong even though they faltered for several weeks, due to the crisis of a center striker. although Nagelsmann had to always rotate his players, he was able to bring Die Bayern out of the center forward crisis, Choupo Moting was the answer to Bayern's need for a pure striker position.
As for Niclas Füllkrug, Bayern Munich are considering the possibility of bringing him from Wender Bremen to the Allianz Arena to find a replacement for Choupo Moting, whose contract is reportedly set to expire this season. Füllkrug is only a ready-made replacement option and capable of occupying the No 9 position, Niclas Füllkrug only fills the void in the reserve striker situation in the coming months before looking for a high-quality striker at the end of this season. Füllkrug may arrive in the summer if there is no breakthrough in negotiations with Choupo Moting before the season ends.
So, I guess the situation is not as you say.