Osmond maybe didn't deserve gold, but she definitely deserved a medal, at least bronze or silver, while Mirai was only 4th at her GP event with a significantly lower score. So I sort of feel like Osmond deserves the spot more, especially because she has a great chance to make the GPF while Mirai has virtually no chance.
As of now, Osmond and Christina Gao are on the same page--both have been unremarkable until this season, and have yet to prove that their magnificent programs weren't flukes. Gao will be at TEB (at this point, I highly doubt Osmond will be getting that NHK spot, especially since Shelepen has yet to announce WD), and I wouldn't be putting Osmond in the "potential GPF" bin just yet. Here are the six highest scores in the ladies' field right now, with 2 more events to go:
1. Ashley Wagner (SA; 188.37)
2. Mao Asada (CoC; 181.76)
3. Julia Lipnitskaia (CoC; 177.92)
4. Kiira Korpi (CoR; 177.19)
5. Kaetlyn Osmond (SC; 176.45)
6. Christina Gao (SA; 174.25)
Others, including Elizaveta Tuktamysheva and Akiko Suzuki, are
highly favored as qualifiers for the GPF. Even with a second GP, I doubt that Osmond would be able to surpass them.