Slipstream requires Garuda, Crimson Cyclone requires Ifrit, damn I guess those abilities don't exist either, why are there even summons? All they do is restrict abilities. Oh yeah, the job's called Summoner.
Imo they need to give SMN way more freedom for when to use summons. Separate all of them, have a different requirement for the little guys like Energy Drain instead of Bahamut, give the big summons - at least ones with utility like Phoenix - a more flexible cost (a cd with charges would work fine), sprinkle in some more options and bam the job's 50% better at least.
Having unique abilities attached to unique summons is what the job's all about but if there's no actual choice in what can be summoned when there isn't much point. Phoenix's heal is there and healers can work around it so it doesn't go to waste but it doesn't feel good or rewarding for the person playing the Summoner because there's no choice.