The sex appeal is the center of gravity of the game. It's the sausage in a hotdog, you still need a bun(story and combat), and it would be nice to have relish(Better pull luck), onions(endgame), and a place to sell it(community support). Without Eula, Raiden, and like characters no one much less people would pull. Lootboxes for guns are nice, but the sex appeal is what drive longevity. Explain to me this, why is Destiny 2 failing but Skyrim SE isn't? One is a single-player game because one has mods including sexy mods, and the other just has guns that get deleted after a certain period, and mask on and mask off ugly characters.
I actually do play Genshin occasionally.
Yes, many characters are attractive and some of the outfits revealing. But as far as "sex appeal as center of gravity in the game", i don't agree. It is still far more subdued compared to Nikke or Raid or even Honkai let alone actual Eroge. Overall it is pretty tame in its genre. There are loads of games out there selling primarily on sex appeal and they all fail to get as popular as Genshin.
And it has many other qualities that might attract or retain users : It has proper exploration that is varied enough, it has lots of story quests and character quests highlighting the ensemble. It has good art and passable music. It is relatively stable and bug free. It doesn't rely on its users to generate content via PvP. The grinding is tolerable. It gets regularly fresh content.
As for what gets pulls ... In the first year (before they made double character banners that are harder to judge), the most popular banners by far were Venti, Klee and Raiden, of whom only Raiden might be somewhat sexually attractive, but all three had heavily figured in stories, Raiden and Venti as archons particularly prominently. (The only other archon, got fifth place). So no, story and power are probably more relevant than sex appeal for Genshin players.
Now Genshin doesn't have ugly characters. It has characters in nonrevealing outfits. It has childlike and actual child characters. But actual ugly characters are missing from this game primarily making money by selling characters.