Balancing Overly Dominant Champions

I hope some Balance Team Rioter can shed some light on this, because this kind of thing baffles me. During patch 6.23, Syndra sported a 36% ban rate (champion.gg data), an 8% play rate, and a 50,5% winrate, across the 25 games the average Syndra player plays.

During the same patch, Kog'Maw sported a 0,09% banrate, 0,8% play rate, and 39 games average across the playerbase. Yet, most likely because his win rate borders 53%, he gets absolutely smashed in the 6.24 patch notes, with a good 200 damage taken from his kit come late game. He's also hit by the Rylai's changes, but that's not part of my point.

Question time: Why is it that Riot has no issue with taking so much damage off of Kog when he's not even played much, not in SoloQ nor in professional play, but just flat out refuses to hit Syndra's retarded single target low-effort damage output - a champion who's been prevalent in both SoloQ and professional play ever since the MYMU's touch-up balance changes?