In Hearthstone, choosing your class is like choosing sides. Here, you're not pledging to the Horde or the Alliance, you're a Warrior, a Mage or a Warlock. Through the expansions, each class receives new cards that can, at any time, change the meta.
What this graph shows us is the evolution of the Wild meta overtime throughout the year 2019 with the release of the different expansions. Unlike Standard mode, all cards are playable, so it is logical that this meta is different from the one you may have known if you don't play in Wild mode!
Druid and Warrior
Very low in the ranking during all the year 2019, the Druid and Warrior classes are the big losers of the Wild mode this year. Not very popular, they have rarely exceeded 10% attendance except for the Warrior class, which saw a popularity pick at the release of the latest expansion: Descent of Dragon — with new cards for the Pirate Warrior deck!
Mage
Ultra dominant since the release of the Saviors of Uldum, Mage has never really been at the bottom of the rankings this year. Secret Mage, Mage Tempo Reno ... All these decks are still very powerful in the meta!