If you only judge a character’s usefulness by what they’re needed for, it’s no wonder people are always upset when they need a character they don’t have.
Farm every character to 7*. If you can equip a piece of gear, equip it. Use Favorites to flag priority characters so the ones you’re actively working on get done faster, but equip everything.
Give every omega and zeta to every character. They give those materials out often enough after a while that there’s no shortage. You might have to wait a whole two weeks between zetas, but the more you apply now the less you need to apply in the future.
Also….. it’s, like…. Fun? Bringing characters up is more enjoyable than letting huge stretches of your roster stay at level 1, gear 0, because in a month maybe a new character might come out.