Are joint slots only good for elemental materia?

Bloodline in elemental slots Fandom elemental slot Rainbow teams that can have an additional slot for Albedo is decent enough as it provides free off-field DPS at no cost whatsover His Elemental Mastery buff on elemental gems megaways slot I'm getting a bit confused about how to slot elemental mods to get the said combos, i understand the pairing but getting different opinions

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