But Thea and Laurel looking to Diggle for confirmation on all of Oliver's calls has nothing to do with anybody's individual mission, especially not Felicity's. It's has to do with Team Politics and who they want to lead them but it has virtually no bearing on how they got there, why they're there and the reasons they continue to stay on the team.
Also I don't think it really matters what the fans think about this kind of stuff. I mean, I don't think the writers care. In my experience of watching this show, these writers have a specific vision or viewpoint and it seems like they don't really care whether it comes across that way, they're gonna run with it anyway. Look at 95% of Laurel's storylines. They never come across the way the writers want them to but they are still clinging to this idea that Laurel knows Oliver "in his bones" and they were "best friends" since childhood. Never mind the fact that they've never shown us evidence of that (in fact they've been showing us the opposite for 3+ years) or that 90% of the audience never bought that crap and never will, it's still something they try to sell as a "fact" in the show (as recent as 4x05) whether we agree or not. Whether it makes sense or not.
So if the show has told us that Felicity's mission is as important as Oliver's then that's the idea they're going with whether the audience believes it or not.