Most of the complaints I hear against Cullen can be applied to many beloved characters. Bioware has shown in the past to have an affinity for bringing back known characters. For my part I think it's because it adds a bit of familiarity to the game, a feeling of cohesion - that you're still in Thedas - and if that has any bearing on the decision to revisit past characters then ALL old friends would be "fanservice". But Bioware also tries to make their decisions relevant to the game or they'd be making a pile of nug droppings. That said, all reasons for not including Cullen could be made of others they have brought back. I don't care for Leliana but I know she has precedent for being there. I don't see a bunch of people vehemently complaining about what her big deal is, though. Most of the "fanservice" and fan-bashing remarks I see against Cullen are from guys. Or girls who bash their own gender the same as those guys - ie. making generalizations and assumptions about the fans. It seems most dissenters can happily overlook the same flaws in other characters that they scream Cullen should die for. I've seen the same, "He's unimportant" and "We've seen enough of him" rhetoric to write a bad trilogy about How-To-Build-A-Seesaw.
Characters that were designed to appeal to the marketed masses seem to be A-ok to most here on the boards despite the parallels they share with Cullen. Leliana gets a free pass for her past - and her overly privileged view of elves, so does Morrigan for how much she never wants to help anyone but herself, Zevran for being a cad, Anders and Orsino are excused to infinity - even Loghain has his fans who still pine for another encounter with him.They're all independent individuals who have been living on their own and making these decisions on their own but Cullen who is part of an organization that preaches a religious rhetoric that the masses live by and he serves an institution that indoctrinates and drugs its soldiers, is held to a higher standard of conscience? He's supposed to "know better" than how he was brought up? Better than a war general? Better than a mage who knowingly took a spirit into himself? Better than a mage who believes in the Chantry and preaches compliance with the Circle? Better than a mage who turned to blood magic even though he had help to fight the Templars? Better than a witch who would help no one but herself? Better than a pirate who didn't return what she stole until AFTER blood was being shed over it and even then only under the "right" circumstances? Cullen is no worse or better than anyone else in DA.
I've come to the conclusion that Cullen haters are just tweaked that a character they don't care for, that is also part of the institution of the "dark side" as it were (rather than a rogue individual) and not marketed appeal to them is something they feel they have to devalue and deny its relevance in hopes that the "It's useless" argument sounds reasonable enough to sway the people who make the decisions.
"Cullen's role could be filled by ANY templar." So could Morrigan's. Empress Celene doesn't NEED her - any dark witch will do but she's a popular familiar face. Oh Maker! It must be fanservice!
Steve Valentine has been tweeting that he's doing lines for DAI... Unless he's doing a different character (unlikely) Alistair will be seen again. But what does the king of Ferelden (or a drunken despot) care if Orlais has issues? Why wouldn't another monarch - like Sebastian, for instance - be picked for a return, or a new one? We could meet the rulers of Antiva! or Rivain! Why Al? *gasp!* It must be... fanservice!
What would motivate Varric to tag along with Cassandra? He doesn't appear to be a prisoner... and once he told Cass all he knew, there's really no reason I can see him hanging around. He was clear about his distaste for the wilds and how much he adored the city - especially the Hanged Man - during DA2 so it seems odd he left... FANSERVICE!
Could it be that Bioware is indeed "servicing" their fans (as much as they're able to and still make a game that makes sense)? Could it be that they think we appreciate a little familiarity to tie the stories together but jamming characters that have NO relevance to the stories into Inquisition would be less pleasant reminder and more "What the frell are you doing here?"
DAI is FULL of "fanservice", if I were to take the criteria used against Cullen as the standard by which such a claim should be determined as immutable fact. That some characters have been seen again versus others with strong fan bases proves that the devs don't just slot characters in because a set of fans have asked. If they are bringing back familiar faces to "tie" the stories together and keep a sense of cohesion to the world and make the story more personable, however; I'd say we're being "serviced" in the best way. If that weren't at least partly true, we probably wouldn't have a Dragon Age: Inquisition to worry about. It'd just be another medieval role playing game. Some people just loooove to whine about not getting everything they want.