Summoner at 90 without leveling!

[Random0]

I've been getting all my jobs up to 90, but have only managed DRG, all four tanks and two of the healers.

Don't panic. Checking your lodestone profile shows that one of the healers you leveled is Scholar. Both Summoner and Scholar are linked due to sharing the same base Class of Arcanist - when you level Scholar it levels your Arcanist at the same time, which in turn levels your Summoner as well. You basically got a free Caster DPS job while you were leveling your second healer.