Those magi that are ranking so high are A) Because the whole raid is allowing them to rank (e.g. letting them spread combustion and other dots that would otherwise not been close enough to do so or other people not killing those adds so the rankers can have greater uptime on them) and B) They are the ones getting extremely lucky with RNG, and a mage with good RNG is stupidly good.
Honestly, I wonder how people don't see that and keep using the "lol magi are ranking so they're so good" argument. (Not talking about you Imnick
)