Not really played much of MMO or FF. I am just working my way through FF7 on the Vita.
Is there a steep learning curve?
Yes, there absolutely is -- but you'll be able to surmount it. It sounds like you're coming to this game from the same angle I was: RPG veteran who knows nothing of MMOs.
I struggled mightily at first, not just with the MMO-speak but with how this game ignores all kinds of established RPG conventions without really explaining this to you. For example, magic elements mean nothing -- you can shoot a fire spell at Ifrit and it will damage him -- Lightning works like poison, and Ice has the additional function of restoring your MP. No idea if other MMOs do that kind of thing, but no previous FF game has. You'll find yourself rotating the same actions on all enemies rather than mixing things up based on enemy weaknesses.
Classic RPG "jobs" also don't mean much compared to the real roles of "Tank" (which sounds like a heavy damage dealer, but in fact serves more as a shield for the other members), "DPS" ("damage per second", which is a statistic but also a name for a
person who deals such damage), and "Healer" (OK, this job is exactly what it says it is). You won't be crossing over much into the other two roles in any given battle or dungeon.
In previous RPGs with enemies out in the field, either they'd see your party and attack you, or they wouldn't. In this game, the concept of individual enemy enmity is now a thing. I played a marauder in the beta thinking it would be a simple physical-damage musclehead warrior type, but it quickly got complicated when the game introduced a fight where the real goal was to take one enemy's enmity away from an ally and towards yourself. Not being able to even conceive of this idea, I lost the fight more than a dozen times as I tried raising my level, changing armor, changing weapons, fighting from a certain position... nothing worked until I learned that entirely new concept.
You also need to press Circle/X/etc. twice to talk to an NPC. Once to "target" them, and once to hear what they have to say. I found this perversely frustrating, particularly because the English translation is so good that I wanted to talk to absolutely everyone.
And the biggest change of all: you
absolutely cannot pause, even when not in a party. Think this is no big deal? At first it was game-breaking for me because when I'm losing a fight or an otherwise struggling with the controls (a frequent occurrence in a game this complex), sometimes I need to stop and take a breath. Can't do that here. Master the positions of everything on your hotbars because the enemy attacks will not slow down while you hunt through them. I don't think I've ever used an inventory item in battle for just this reason.
This kind of thing really adds up and can be frustrating for the newbie. I don't think I would have stuck with the game if not for the helpfulness of GAF.
From an MMO veteran's perspective, the large amount of soloing early on probably serves to ease noobs into it. From the noob's perspective, I still think that a lot of concepts weren't explained well enough.
I actually recommend starting out with one of the crafter jobs, which you know going in is going to be nothing like typical RPG combat, and wandering the world and mining metals and weaving clothing.
It's a fun game and I recommend it to anyone -- just put aside everything you know about RPGs and previous FF/S-E games, because this game is its own beast. Allow lots of time to learn the ropes; it's worth it. But it never really stops being frustrating at times.