The fact that there was no evidence shown that Starlight could actually hurt Tirek, whereas Twilight actually made him lose a tooth, in contrast to Star Swirl accomplishing nothing at all, should be the nail in the coffin on that particular debate. Twilight is
probably stronger than Starlight, and by S9 would likely be skilled enough to defeat her, solo. Maybe
Starlight would outperform her at first ala anti-boosted Chrysalis style trickery, but Twilight would quite possibly be better at keeping up with her than she was.
In RPG terms, Starlight would probably have great Intelligence and Agility stats. Or some equivalent thereof.