"MMORPG" is a stupid term, and "MMO" is even worse. There's no consistency across the internet, and there's no actual basis for the meaning.

No, you confusing usual ignorance with lack of an obvious definition, which is primarily shared, active gameplay within a persistent world with a not noticeably limited, crowded server population. Shorter: shared gameplay in a persistent, crowded world.
It's that easy, it applies to MUDs, Virtual Reality or any future abstraction of the genre.

"Massively multiplayer" has been a more applicable term to several FPS games in the past 10 years No one's using massively multiplayer, and companies push the term MMORPG or at least MMO whenever they can, best recent example is Destiny 2.

Yes, it can be indeed a bit difficult to decide where to draw the line between a large multiplayer and an MMO, e.g., Wurm Online, but in most cases that is not the reason the term is misused.

DFO is definitely not an MMO, it's a lobby-based multiplayer. A chat with access to everyone doesn't make a game an MMO, or all Blizzard's battle.net games could've been called such.