Only the cheesecake now is authentic of the desserts; the rest is not, and much never was. Frankly, the quality is really continuing to go downhill, and often we are finding stale food (and the staff whispers at me in German not to eat it) Items appear to be left out longer on the buffet before being replaced, and many entrees and salads are not on offer ie the selection is reduced. That is my own observation over the last six months or so, combined with feedback from the servers there.
My local German bakery in China is far better than Biergarten these days. I was once someone who recommended it with a strong disclaimer that it was not authentic German food but decent Americanized food 'inspired by' - I can no longer even say that.