I'm just judging by my own experiences from different social media. The only fans who mention/praise/ask for OTA on the producers'/actors' twitter timelines are Olicity fans, which is very apparent from their avis and aliases. The same applies to Olicity-heavy fan spaces like tumblr. The small part of the tumblr fandom that isn't Olicity fans do not make OTA edits, or write metas about this particular constellation. The fans who ask Stephen Amell for OTA pics on twitter and Facebook are also exclusively Olicity fans.
On many large online discussion forums OTA is very seldom a subject of discussion, and it's hardly ever used to denote Oliver/Diggle/Felicity, probably because it's not considered altogether correct (although promoted by the writers and actors as show "canon"). There are even fans who consider Oliver/Diggle as the true original team, since they worked together as a team from episode three until episode fifteen, when Felicity officially joined. In general I'd say that Roy, Thea (and sometimes even Laurel) are considered just as important and interesting as team members as the "core" of O/F/D.
I guess that there are many fans out there who don't regard Oliver, Felicity and Diggle as the hub around which the show evolves. But that's true of every fandom, isn't it? People will feel differently about different aspects, characters and storylines. My enjoyment of the show is not dependent of the amount of shared scenes (or common storylines) between Oliver, Felicity and Diggle, because I don't think their interaction is more special than Oliver's interaction with Thea, or with the other characters close to him. I liked seasons one and two as well, with the early Diggle/Oliver scenes, and I thought both Roy and Sara were great additions to the team. Seasons three and four were pretty disappointing IMHO, but not because Laurel and Thea joined the team. As for the current season it's not really any worse than season four, despite the arrival of the newbies, and some things have improved, like the fight sequences and the plotting, at least in my eyes.