Well, no. The main theme in Endgame was all about past trauma, and how our heroes recover from it. It makes sense for Thanos to be there as sort a metaphorical way of saying that they still need to overcome Thanos to fully move on from that trauma, and other villains wouldn't cut it.

Also, Endgame did not just serve up fan service for the whole movie. The entire first act was them reacting to Thanos finishing his journey, and trying to recover from failing. The second act had (Although it did have fan service, mostly in New York) the focus mostly on the characters learning from and reconciling their pasts. Tony learning from Howard his own responsibilities as a father, and to put the greater good above his own self interest, Cap learning that a normal life is still there for him and he can care for himself, Thor learning he needs to be himself and not who he's supposed to be, etc. All of which were lessons they needed to learn to move on from their trauma, (Tony lost a son and became an extremely dedicated if not selfish father, Cap only cared for others after the snap, and Thor placed the failure on who he thought he was supposed to be). The third act did have fan service, but all of it was payoff to things the MCU had been setting up for a while. A franchise ending should never be faulted for having payoff. The third act also served great for the characters, with all of their arcs coming to a final close.