Historically summoner has been competitive with black mage, the highly questionable decision to nuke it and all complexity it as much as looked at has left the caster role in this absurd state. Black mage and summoner can no longer exist in the same niche without a major rework of one or that niche being conspicuously broken. Summoner being more braindead than red mage, the designated easy caster. Given past justification for inflicting reworks, it seems black mage should be next on the chopping block (low player count, modicum of skill required, been as it's been for ages, not fitting in with the 2min thing) but we all know it won't.
Each member of role - caster, ranged, punchy, healer and tank has to provide roughly the same utility (damage) as the others because there's no other metric that affects ease of clearing, particularly with the overreliance on body checks this tier. Summoner and black mage being such polar opposites in skill requirements means both deal the wrong amount, black mage being undertuned and summoner significantly over. 2 minute buffs have not helped this in the slightest, but I think it's more likely to be two things going wrong simultaneously than directly at fault here.