Alright, thanks, that makes sense. I can just tell you my anecdotal "evidence", namely that despite the supposedly too high layer height and the messed up infill, the spool holder is really strong (I tried to break it b/c I thought it might not be strong enough).
Regarding my original question: I think I understand now that you are probably both right! I just looked at my gcode at gcode.ws and I see that the full hexagons are indeed printed along two alternating diagonals (Which is what @Phaedrux wrote and rather I misunderstood them) + then it might make sense that with a high infill speed and too high layer height it just did not manage to squeeze out enough filament and thus the infill was sagging? (Still, perimeters are fine, but they are printed more slowly.)
Honeycomb and some of the other nice looking 3D patterns aren't especially strong and they print slowly because the direction keeps changing. If you want strong infill that prints fast, try grid or triangles
Thanks a lot! 👍