As mentioned, just because you have all elements, doesn't mean you can't have more priority on one over the other. It's better to have at least 1 or 2 very strong teams that can handle the difficult content with little problems than it is to have 6 teams that struggle. Of course, this is assuming you're not a whale, cause if you are and is one to spend a bunch of money, then this becomes irrelevant.

I have a team of each element and my main element is light which I use to handle all the hard content such as advent Ragnarok stages and advent events in general since they're far more difficult than raid events. Elemental advantages help but they're not always needed and variety is a good thing to have but when it comes to raid events, all I do is tab away with auto battle on. Not exactly much of an different experience.

And back onto the question, I would also only pick Belobog only from that list as she's a healer so you'llmost likely use her more often, unless you have Sol. Not the best but still viable to a degree. You'll want to max out any girls you use in general but it doesn't hurt to save a few in case you get lucky with other draws.