@Azyrite
Ideally, Starlight and Sunset would take turn being the leader and lancer, sure.
Unfortunately Sunset is gone too far into the Main Lead role that whenever she plays lancer, it feels like she’s not doing much. Meanwhile Starlight is an excellent Lancer/Dragon but whenever she takes lead role, her personality makes it hard for most of the audience to root for.
I.e. Sunset is a terrible lancer and Starlight is usually not good at lead role when there’s somepony else.
I agree SunStarTrix would be very fun indeed. I can dig that, why not. I’m just saying their dynamics probably wouldn’t change very much. I mean look at StarTrix: the duo plays out more or less the same way.
Meanwhile SunTwi and TwiStar don’t play the same way all the time, reason being that all three of them are spotlight heavyweights, so one one will have to give way to the other. Two are THE central characters of their own series, while one is…definitely a very prominent character, no doubt. Which means one of them will have to play the clown/foil/comic.
Honestly, Starlight and Twilight can handle being the Fool. They’ve been on the butt end of jokes and they’re very quirky, while Sunset will probably be the straight man as always.