Just for fun I looked up how many solo comics, set in the main continuity, with their name on the cover Vixen and Zatanna have.
Vixen has only 6, a 5 issue mini and her Rebirth Special
Zatanna has 26, a 16 issue "ongoing", two 4 issue minis and 2 one shots.
When it comes to the popularity on webtoons, WFA has (when I understand the stats on webtoon correctly) about 47,6 million views, so a little over 1 million per free chapter, Vixen has just a little over 640K views, so about 80K viewes per free chapter.
So WFA has about 12-13 times more readers.