I agree with you wholeheartedly with Sunset's redemption. And while I do feel Starlight's was fundamentally better, it still just doesn't work for me.
And this fury consumed her so much that she was willing to flat-out destroy the possibility of a non-apocalyptic Equestrian future, all so that Twilight would never become friends with the mane five. And this isn't something that's simply negligible and can be swept under the rug. This is serious. This is how bad her "fury" can get---that any humane feelings towards her actions can be instantly negated by nothing more than something as simple as envy. In this case, it's envy that Twilight's friendships are so crucial to Equestria's future.
Bottom line, Starlight is a borderline psychopath, and there is NOTHING her last-minute reformation did to convince me that she isn't still a borderline psychopath. That she doesn't still have an underlying fury that most certainly needs to be addressed before she can hope to become a recurring character, let alone a main one.
Hell, she flipping laser blasted the filly Rainbow Dash less than ten minutes before her reformation occurred. I mean, come on.... :okiedokielokie:
And yet, what irritates me the most is that it seems as though her road to redemption is finished. That she isn't going to go through a period where the mane six mistrust her like Discord did, nor will she go through a period where she has to legitimately earn the mane six's forgiveness. We're apparently supposed to believe that after years of holding unwavering views on cutie marks, she is now 100% changed after a simple and quick "it won't happen again" speech and that the mane six have no reason not to give her their unwavering trust right away.
Just doesn't seem right to me....at all.