Always use Obey as a Scholar. I can sum it up as follows:
▶ Fey Illumination: Your 10% healing potency buff should be saved for boss fights and big pulls. This should be saved for when the party is starting to take a lot of damage and you need to spit out heals stat.
▶ Fey Covenant: Your magic defense buff should be saved for predictable unavoidable party-wide AOEs during boss fights. Blowing this on trash pulls and at the start of the fight before the AOEs come is basically wasting the ability.
▶ Whispering Dawn: Your AOE heal is on a quick cooldown and can be used on every other pull (or every pull if the mobs are dying slow).
The AOE Esuna is for when there are 3+ status effects on 3 or more different players. This ability is more useful in Raids where there are a potential 8 players with negative status effects on them.
Silent Dusk is super situational. I honestly find very few things that this silence applies to, and I'm too busy healing to experiment with silencing every mob to test out what it applies to. Most bosses are immune to silence/stun so I find it pretty useless.
So for Eos 2/3 abilities need to be timed to be effective, and with Selene 2/3 abilities as well. So you need to put your faeries on Obey if you want to be maximizing their skills. If your gear are bad, then you have to spend a lot of Final Fantasy XIV Gil on it.
As for Summoner you can put Ifrit and Titan on Sic and let them auto-pilot. Titan is just for soloing overworld content so it doesn't really matter how optimal it is. Ifrit has nothing that needs to be timed just let him do his dps. Garuda needs to be on Obey so that you can time your Contagion with your burst damage (Bahamut, Deathflare, Tri-Disaster, Festers).