2010 oldfag here.
People shitting on the show, characters and fans have been around since the first /co/ threads. They've just grown in numbers and have evolved their tactics to look like some kind of thing /pol/ would think up. It's gone far beyond than just saying "this show is shit" and "your favorite pony is shit". Now they worm in, pretend to be fellow fans disgruntled by the show's direction, and pen this script where the showrunners are deliberately trying to run it into the ground and hate their fans. And then these fuckers turn around and attack anyone who praises the show with buzzwords. In 2010, we could really only call these kinds of people "parasprites", but that seems like such a quaint insult now.
Starlight has been an easy target because indeed, even among fans, there's this feeling her reformation at the end of season 5 was rushed. I have a feeling they wanted her as a recurring antagonist, but The Powers That Be pushed to have her as a protagonist. That said, her character development afterward has been an improvement and she's grown on me. Nonetheless, this one thought of her role as hero or villain has been ballooned by these fuckers into "she ruins the show",If anything, this show has always been riddled with flaws and never really goes as far with its story and lore as it could, but considering it's Hasbro in charge, that's ALWAYS been the nature of this beast. This is something you need to accept before even starting to watch this show.