Originally Posted by
Absurdity
Not sure if I would really call it fanservice.
All Final Fantasy games have recurring characters, locations or ideas to a certain extend. Be that Cid or Biggs and Wedge, primals like Alexander, Odin or Bahamut, locations like Ivalice and the Crystal Tower, ideas like Aether or the Warrior of Light.
Those have all been in one or more FF games in the past, the difference is that these are still integral parts to 14s world and story. They're integrated into the universe of this game in a way that makes sense, often with explanations on why they're here and what purpose they fulfill, expanding on what we know about the world.
Can you say the same about most of the collab events? NieR was basically explained with "they came from a different universe", same with the FFXI and the FFXV event, a lot of the other collab events don't even get that much.
This is what I mean when I say I couldn't care less about collab events, they aren't integrated into the lore, they don't tell us anything new about the planet of Hydaelyn, they purely exist to have us go through a 15 minute quest and give us some fanservice rewards.