Hear hear. OP just doesn’t seem to grasp it, no matter what everyone says so it’s almost not worth typing this.
Until they stop singing their usual verses in the theme song, somehow lose their thrones around the Cutie Map, or we stop checking in on their characters and stories, Twilight, Pinkie, Applejack, Rainbow, Rarity and Fluttershy will always be the Mane Six, you can tell by all the group shots of the six standing together, and Spike has always been a main character since day one, he has a throne too. Starlight Glimmer is an additional member of the Mane Cast summoned and featured when required, no different from CMC, doesn’t mean she’s stealing Fluttershy’s and Pinkie’s places. Who but the Mane Six and Spike were summoned to Tartarus? Who had seven intersecting stories in Best Gift Ever?
Dear God, Starlight always has to share her episodes with Sunburst, Discord, Trixie, Twilight and the others anyway. Fluttershy can literally carry the better portion of an episode with just three racoons and Pinkie can even receive the status of second most prominent M6 in the movie and her playing a yovidaphone (even if you hate the episode, OP) is given the life or death attention and concern by the others.