The story of FFX-2 is in essence about Yuna being stuck on the loss of Tidus, not being able to move on and not able to enjoy the peace she has brought to Spira. She chases someone she presumes to be Tidus, but ultimately isn't, and through Shuyin and Lenne's tragic story, she is able to get a sense of closure and move on. The normal ending FMV ends on this very note; she didn't quite find what she was looking for, but in turn, found something else and was finally able to move on. It's bittersweet, but it's uplifting and leaves us with a happy, content Yuna. The whole story builds towards this conclusion and not a reunion with Tidus.
Of course, if you mash a few buttons in the farplane in chapter 3, and say yes to the Bahamut Fayth's Tidus Resurrection Service, then you'll get your pure fan service ending. I don't think Tidus appearing briefly on the Farplane goes against him swimming in a new ocean, or whatever it was that the Fayth said. Tonally, what the normal ending and the good ending represent, it's pratically oil and water. They do not mix well at all. I always thought that it was blatantly obvious in the way they handled the good ending that the story was never really about Tidus and Yuna being reunited. That ending was fan service they felt compelled to deliver as an aside to serve a certain part of their audience.