The correct answer should be Magnezone.
That image you provided looks like a raid simulator against Blizzard Kyogre. When you're in raids, DPS matters more than TDO. So Raikou with TS/WC will always top Zone in that situation (As will Electivre as an example). However, if the question was which is the better "counter" then Zone will be the winner as it's Steel typing allows it to resist and take hits from Blizzard.
So you are correct. While Raikou will always do more damage, Zone is the better "counter" since Raikou will very likely not survive a Blizzard.