Bell didn't really want to pick up girls what he really wanted to be was to be a hero like the ones from the stories. It's just his pervert of a grandfather taught him true heroes have harems.
Besides it's obvious that Bell wasn't the true Hero protag but actually the main Heroine in Ais's harem.
Lili and Bell both seem to fit the Familia rather well, given how things are going.
Interaction-wise, Bell drops another "alien common sense" member in Hestia's lap, because at this point she badly wants some NORMAL familia members. Meanwhile, Lili ends up as the semi-normie in the room who gets to comfort and or share a freak-out with Hestia every time QA and Bell do something absurd.
Lili's whole thing at the start is wanting to get free of what amounts to the Danmachi version of the Merchants, but she can't because she's not allowed to talk to her god, and even if she could he's a self-absorbed asshole. (Which explains why a rando level 2 with a shoddy flame dagger is running the place, nobody gets Falna updates.)
Problem with that
now is that Ishtar just got hit with orbital lasers over a similar problem.
Odds are that current Lili can slip past everyone, talk to Soma, have him actually feel bad about how his Familia has turned out this time, or at least deeply concerned about the potential consequences and their impact on him being left alone to work, followed by Lili showing up to join Hestia Familia herself with no canon "free Lili" arc needed. Unlike the Ishtar refugees, Lili isn't incapable of going up to people.
Lili joining after fleeing Soma Familia would also get the Ishtar refugees thinking "wait, we can just do that?" which could lead to some of them getting closer in, setting things up for Haruhime and Aisha to turn up together and ask to join once things with Lili and Bell are mostly resolved. Lili joining gives Hestia the impression that things will be normal, then Bell shatters that, then QA makes Bell even worse, then Haruhime and Aisha join after that chaos settles down a bit. Or they join in the middle of QA halping corrupt Bell, and being bemused by the chaos, but happy to be there anyway.
Bell, on the other hand,
just wants to be a hero. Which fits because that was literally Taylor's shtick, starting out. I could easily see QA setting him straight then taking Bell under her wing while indoctrinating him on her very strange take about what that means, as Dreamer!Taylor is ROFL in the background and adding fuel to the fire.
We still get Bell, it's just that his "oblivious harem protagonist" flag isn't going to last long. Even if QA didn't kill it by sticking strange ideas in Bell's head, Bell's harem route wold catch fire the first time QA tried to ask about whatever girl was showing interest in him. Persistent directness, especially when Hestia's asked Bell to help QA with human interaction, is not going to stand up well to oblivious harem protag "it's fine if I never confront it" behavior.
Tossing Bell into another familia just ends us up with a wandering harem protag with a literal plot armor attribute on his status, made worse by being raised by probably Freya thanks to her eyes thing and tendency to poach. Letting QA reform him kills the harem route bullshit dead, keeps him from trying to horn in on QA/Aiz goodness while Luck helps him turn up at the most annoying time, and gives QA a cute little brother to teach horrifying things to. It works out good.
(There are plenty of alternative routes, but this was my favorite)
