AC started off as single-player only in the first place anyway. It means I'll actually have a chance at getting all the trophies this time as well. The online-only trophies from Brotherhood onwards meant the Platinum trophy was always out of reach for me since I didn't play the MP.
I'm not sure what you did in ME3 since I along with a lot of other people found that there simply wasn't enough "war assets" in single-player alone to see all of the outcomes. BioWare themselves confirmed that this was a bug and the Extended Cut DLC fixed this issue.
In a single-player game you should be able to 100% it from playing single-player alone with no multiplayer or smartphone apps involved. If I wanted to play a multiplayer game I would have played one to begin with. Some games are just better as single-player only experiences in the same way some games are better as multiplayer only experiences. People play games for different reasons.
I enjoy games like Titanfall as much as other people do. That doesn't mean I need Titanfall style multiplayer in every game. I enjoy story-driven games as well but that doesn't mean multiplayer games like Battlefield or Unreal Tournament III need 5 hour single-player campaigns since it's not what those games are about. They just end up feeling like practice modes for the multiplayer.
ES496's comments