Why do Scholar's job quests still require a level 30 Arcanist to start?

[Gemina]

I don't understand why people think Arcanist flows into Summoner

Summoner has absolutely nothing to do with Arcanist, even remotely, and never has. If anyone needs to be detached from Arcanist, it's Summoner.

Perhaps it's because ACN is a DPS class, and SMN get to [sort of] keep Carbuncle. Early day SMN also wasn't like how it is today, or going to be in EW. The old mech of casting Bio and Miasma and then spreading them to all targets via Bane, and also Shadow Flare and even Aetherflow were all ACN skills, so SCH and SMN retained all of them upon receiving their respective Soul Stones. It was actually SMN that expanded the tactical DoT mayhem with abilities like Fester and Tri Disaster, and their Egis bringing a steady DoT through their auto attacks, and also possessing DoT inflicting abilities of their own; so I wouldn't necessarily say, "Never has."

Despite all of that, I agree with you somewhat. But the way I see things is both SMN and SCH are ACNs. Lorewise iirc, both of them bring forth Egis and Lily respectively by channeling their own aether to retain their forms. A big difference being that SMN bring forth an essence of a primal and its an extension of themselves that they can command like an arm or leg; Lily however is the actual familiar, whom is sentient and has a will of her own. Who I don't agree with are the devs and their decision to try and rip this identity from SCH, especially at the cost of making ACN nearly unplayable levels 1-30; especially if you leveled it back in its prime.