To me the mere presence of a familiar character or ship or whatever doesn’t really qualify as fan service, so long as their inclusion makes sense. Otherwise the existence of the movie(s) itself is fan service, which, yeah, I suppose so, but maybe the distinction here is good fan service vs. bad/misplaced fan service.

Bad/misplaced fan service would be of course a character or ship showing up that doesn’t make sense for the story or if there’s too many or they put too much undo emphasis on them like Evazan and Ponda Baba in RO. Like, if Boba Fett shows up, fine, we know he and Han run in the same circles. But the key is to make sure he’s only given as much importance as the film itself supports. I could imagine a scenario where he shows up and does something cool yet unimportant and vanishes like Hawkeye in the first Thor movie. That, to me, is bad fan service.

Darth Vader in RO comes dangerously close to this, honestly. All of his scenes are narratively dubious but at least it makes sense for him to be a part of that story. And, though some may disagree, I don’t think they prop his character up to be too much more than he actually is.

That’s the other fear with “fan service,” taking a character everyone loves and making sure they’re 110% cool and bad ass throughout (more so than the character actually is). They’ve done a very good job with this thus far, I won’t go into TLJ spoilers here but that film completely dodged the easy and obvious bad fan service bait with Luke Skywalker, which I’m very grateful for. They did the same with Han Solo in TFA (besides one very small moment), so for the most part I trust they’ll do his character justice here.