A lot of people are more cautious about Sage than optimistic or pessimistic.

We know more about sage than healing as a whole atm, and that's why everyone is in wait and see mode if they aren't an Astrologian which are in justifiable panic mode.
We know the following: its got shields from Astro and Whm's lost self buffing niche. Its AF gear, weapon and poses. It will start at 70 (ofc) and so their first levelling dungeon is going to be the difficult hominister switch with its mass of scorpions near the start.

Meanwhile what we don't know:
Will shields finally stack or continue to be inferior to raw hp?
Will healers get some resemblance of a downtime back aside from pressing 2, 1, 1, 1, 1 etc or will we be stuck as "pure healers" again
Will the stat squish be weighted to make healing requirements heavier or are we gonna be in the same state as before with 75% of our buttons being dps
Will mp become a resource again rather than just a limit on raises?
Are the devs going to acknowledge and fix the monumental volume of problems on healers they added in throughout stormblood and budgetbringers or double down on them?
Are the levelling kits going to be fixed at all or will they still have less going into sastacha now than they did back in ARR?
Will Sage be a magical girl with lasers instead of glitter, or will it be a proper techy healer thats not overly feminine for a change?
Will healers start moving away from being in nightwear and robes and into armour or are we going to suffer in the glamour department again?
Will whm get its elements back and expand on the lillies or will they delete assize and misery for not being "pure healer" enough?
Will sch get its fairies back or are they gonna be further butchered and try and delete energy drain again?
Will Astros get their time magic and cards back as compensation for losing noct sect?

I could go on but you get the idea. They haven't given us much to work on, and their recent reasoning and statements do not give cause to be optimistic for the current 3. Sage is a different beast since new jobs are always more flashy and varied to entice players to try them out so it could well be a scenario where sage is fun but whm/sch/ast aren't