were you on a nonextraction plan for decompensation?
you can always get more decomp if you extract premolars. In case of your underbite, if you extract upper premolars and retract the upper front segment, you can advance the upper jaw much further afterwards than without extractions. You would also have had a truly massive underbite after decompensation right before surgery. Judging from the pictures you provided, Mommaerts didn't have enough room to put the maxilla in an aesthetically pleasing position. So he moved it forward as much as possible while retaining proper occlusion. That's not really a surgical error but rather poor planning between ortho and surgeon - if you needed extractions for decomp and didn't have them.
Of course such things require good teamwork between the ortho and surgeon, not sure how this would work with a belgian surgeon and a swedish ortho. I know the general consensus in this forum regarding extractions, but I have come to believe that for optimal results they are (sadly) necessary. At least in the jaw that's deficient, i.e. class 3s need upper premolar extractions + bimax and class 2s need lower premolar extractions + bimax.