As for Starlight, just as she said. With Sunset still alive, it seems this universe’s version of me and Starlight grew up together as Celestia’s students. Thus, we were groomed to be the next pair of Alicorn “sisters” for when it was time for Celestia and Luna to retire. Starlight would’ve had a much happier childhood. She’d had never did the Our Town equality cult, and most certainly wouldn’t have time traveled.
I can’t tell from here what would have been the other differences. It seems I still met the friends I’d make in Ponyville. I don’t know how that effects the Elements of Harmony given I doubt Sunset surviving her encounter with Cozy’s family would go as far as creating a 7th element. Maybe somehow me and Starlight shared the Element of Magic together, or even if Starlight wasn’t an element… she still assisted on our adventures in some way. It’s at least very possible either way that Starlight got her own throne at my castle after we defeated Tirek. Since it did give Spike a small seat