About the Sunset Shimmer topic, I admit I wasn't interested in her. In the first movie she was a very basic villain. But, even though I don't consider Rainbow Rocks a good movie, the fourth EG film made me appreciate Sunset Shimmer more than I expected, like a lot.
I don't think Starlight is a "spotlight stealer" (it's a very empty line, whatever you call it). However, I think she has less character development than needed (2 episodes in season 5... yikes), more magic power than needed, everyone in Ponyville is completely supersticious about her actions, she repeats the same line "I was bad in the past" in season 6 more times than needed and, in Every little thing she does, as someone who wants to redeem herself, her will to finish her friendship homework as quick as possible doesn't fit with her desire of redemption.
If it wasn't for that episode, I'd probably have continued watching the show and finishing it, even after the redesign of the changelings.
It doesn't really matter though because I accepted that the TV show is just a procedurally-generated story getting more and more off the rails.
As a result, I just stopped.
Before I finish, quick disclaimer: I don't think Starlight fans are clueless or idiots. That's a dumb thought. If you think she's a great character, that's great. I just wish she got a better character development in seasons 5 and 6 instead of just waiting for one or two seasons to get to the real point.
And, redweasel, I understand the disappointment, I get it. However, if something disappoints you, try to be cool about it, try to take it easy, don't write your thoughts in the middle of the heat.
Whether you love Starlight or you don't, take care everyone. ;)