I think they were always supposed to be a team. Sunburst has the information, and Starlight has the power.

@soundtea  
Hmmm. Now that you say it that way, I feel sorry for him. Here he is, sent to what basically is pony Harvard just because he received his mark only to learn his abilities to cast magic are between diddly and squat, but has to keep up appearance for the sake of his family,decided to become something by acing in other fields like actually knowing about magic and spells to make up for his poor casting ability, but most likely dropped out due to both the pressure that was heaved up on his shoulders by his folks and the fact that “wizard diplomas” are for, you know, casting spells, and decided to head as far away as possible from any contact with folks back home (way way up north) because he didn’t want to confess that he ended up not being a wizard and that getting his mark was a fluke.
 
Pity, though, if he didn’t return home, Starlight wouldn’t have gone on to become the mark-hating dictator of a small commune and/or tried to erase Equestrian history.

@nobody here  
Sunburst never got an invite, he just took his sudden cutie mark get as a big sign and his parents sent him off. Then he realized that moment was pretty much a fluke.

@soundtea
 
Not just that… He’d do something, show her a page in a book, then she does it better. Celestia, why no invite to your school for Glimmy Glam?

Looking back at the flashback, it seems Starlight always had the raw power over Sunburst.