Sage is not remotely true to the established job in final fantasy. I therefore propose that it should be nuked harder than summoner and turned into the black-summoner-white-mage that it truly is. They could function as a healer that requires black magic spells to build toward summon tokens, which would be essentially 30/60/90/120s cooldowns. Naturally this would necessitate some way to rapidly build the tokens at the start of the fight - ie an actual opener. To avoid overcapping, a dps neutralish way to convert them into damage would also be needed. Beyond that the white magic could cover the standard healing e.g aoe heal/single target heal/same but ogcd/some kind of regen.
This would also allow the job to have names that aren't all greek to everyone, something that for obvious reasons should be reserved purely for the ancients and their nonsense.
If bootleg dark arts is integral, using a non-greek eukrasia could swap certain non-core spell effects between black magic/summons or similar.
This leaves scholar free to occupy the scholar niche, and ast can have sects once again.