I love them and they’re my OTP but I also know that Rumbelle was a huge fan service–they wanted to do the story but after Skin Deep became the phenom that it did, A and E were salivating to keep Emilie around. Even Emilie admits that the Rumbelle fans are pretty much responsible for keeping her around. So, while CS doesn’t speak for everyone–obviously–they do have a pretty loud voice. Can A and E block that if SF was always their original plan?
Rumbelle is a totally different situation IMO. It’s unlikely that they had any other plans for another potential romance for Rumple. And Emilie is a friend of theirs. So when the fans demanded more Rumbelle, they could easily adapt their original ideas, and instead bring her back. I’d think that they already had that possibility in mind anyway, considering they actually had Belle locked up in SB in Skin Deep, so they’d set it up for her to potentially be around in present day if they wanted to use her more. They probably thought they’d throw out the idea of Rumbelle, and if people liked it, they’d do more with it. And it turned out people really liked it, so they did more with it.
In the CSF situation, if SF had been their original idea for endgame, they can still get there, even making a few detours along the way. Do any of us believe that an original SF endgame plan EVER involved smooth sailing and a quick, happy reunion? If they really were originally planning on having Emma get involved with August, then they were already planning a triangle-ish detour for SF anyway, they just changed the route that the detour is taking when they decided to go with Hook, (due to his popularity with fans) instead.