You'd think so, but FF14 has proven to me that a great story can be told pretty well within a MMO. There's not much padding either or wasted time within 3.0 and 4.0. When the story is building up toward something, it does go quick and I think it's due to the game forsaking a fetch quest for a solo instanced boss fight, a dungeon, or a 8 man trial. Those alternatives are far more interesting. Also, there are quests where you simply watch well done cutscenes, which I'm cool with.
Actually, FFXIV has shown to me that the MMO format is potentially the
best platform for telling a good story. There's an amount of expansiveness in XIV that you will never find in a regular mainline FF title.
FFXIV has to deal with padding sometimes through the meat of the main content...but what you get between that is a world FULL of NPCs, settings, situations, ect that provide you with lore and characterization. It's something that simply
cannot be feasibly matched in a regular RPG experience.
Every class, job, gathering and crafting class has its own storyline, which builds upon the lore in its own way. These characters exist within the world and even end up in the MSQ on multiple occasions. Every location has a purpose, backstory, and history, many of which (most of which) are explored through some questline. Some of which are covered when they're shown, some covered in different updates or future expansions. And even if you're in the middle of a questline and the developers haven't finished it yet, there's still a literal world of content for you to bother yourself with if you feel the need to.
What usually happens when Square Enix tries to mimic this level of lore depth? You get situations like FFXIII's datalogs or FFXV's need for supplemental material to explain things to you.
Not because it's impossible to cram into a single game, it's
possible. It's just that it's incredibly difficult, and the more complex everything is the more you have to sacrifice in a single development period (and a measly 40 hour game time) to realize to its fullest potential. The truth is that most of Final Fantasy's storylines up until the recent days just haven't been as fleshed out as the ones releasing today.
For a game like Final Fantasy XV to have released as a single title containing all the information covered in Brotherhood, Kingsglaive, Kings Tale and the demos, the game's plot would have had to have been expanded so far that it likely would have resembled a completely different game.
FFXIV's relatively boring fetch quests is what actually allows it to have such a expansive lore the way that it does. Even if every single cutscene was voiced and motion captured, it simply wouldn't work in a regular RPG. There's too much info.