You'd have to play very little XIV, or be some manner of TT/LoV/BT/GS competitionist, for the majority of your time spent to be in solo content, let alone 80% of it.
The same is true of WoW, Rift, GW2, B&S, Neverwinter, and (though more variably) PoE.
When design decisions are made to curtail complexity at the new level cap, to the result of negatively affecting the sense of player progression or toolkit cohesion at earlier levels -- i.e. when you improve A (endgame) at the expense of B (everything prior) -- we can say that endgame is their priority. That much hasn't occurred in each of the MMOs I've listed above, but it certainly has in, say, WoW... and a fair bit here (though it's always been notoriously unwilling to give much to early levels).
