4 may have sold more than ARTPOP but it was a lot messier. The album leaked a month before its release date and Bey was randomly dropping videos to a point where you couldn't tell if it was a single or not.
ARTPOP had Applause, a standout hit that was very successful and Do What U Want, a hit that was still bigger than any of the singles from 4.
ARTPOP derailed in the latter end but it started off decently. Aside from the first single leak, there was decent momentum.
I lived for the ARTPOP mess. Venus vs DWUW, the little monsters 260k meltdown, the gifs of 260k and every base uniting to scalp monsters. The DWUW video wait, whatever G.U.Y was.