Obviously the visual effects work (and presumably the score) were unfinished or nonexistent at this stage of these screenings. Usually these type of screenings are used for editing and pacing and determining what the audience response to as they don't want to finalize too many effects if they need to make any major changes to any particular scene or sequence. Probably kept major twist details private from public screenings. They were likely going through different cuts of the film to see what received the best response which would explain 1) the different test screening reactions (if you remember one screening had positive reactions) and 2) conflicting leaked info on certain characters or plot points. Different cuts.
I remember with Days of Future Past, people were really negative about Quicksilver's look thinking he would be the worst part of the movie. There were also complaints about the redesigned look of the sentinels before the movie came out as well.
Production design (look and feel of the movie which includes creating the initial concepts, building sets, fabricating costumes, developing makeup effects, and working with the VFX team).....are all based on the director's vision. Everything is approved by the director. So it isn't a matter of hired artists not being talented enough or numerous enough, but rather how the director envisions the look of the movie and translate that to the production design team who all take their cues from the director.
