It doesn't have tier 0 winrates yet, does it? Mobalytics high winrate build is 54.7% which is good but not even close to what like Sivir/Akshan were pulling.
The nerfs might change that but it isn't there yet.
A few factors to consider:
*Most players are still playing unrefined versions of the deck and random piles. That is deflating the stats, the versions that are refined are pulling in tier 1 winrates.
*The deck actually wins or goes even against most match ups. It specifically beats Akshan Sivir decks and it also beats Ezrael Draven. This is not reflected as well on the stats but you can check pro player opinions and matches to see, which brings me to my next point. I think only specific control decks and Bandle City decks can beat this deck consistently or if you can manage to go faster than it.
*This deck is actually kinda hard to play. Not Lee Sin or Karma level but at least around Ez Draven level, probably more. That's putting a limit on its winrate.
*It's the most played deck archetype in the game right now which means a lot of players who aren't as skilled using it which always skews winrates down. It's like the early Azir Irelia problem, Riot was claiming that WRs were trending downwards and that was because every type of player was joining in on the bandwagon. This takes time to stabilize.
*Most of the top ladder players right now are Sion Draven players and its making a high percentage of the top spot.
Of course this is just one side of the argument for why it might be the best deck in the game. Here are arguments against it:
*Since there are so many versions of the deck out there, it becomes hard to play around and tech against it. The deck can be played in numerous ways and once a singular deck crystallizes its difficult to target.
*The decks that might do well against it aren't well represented yet because the meta hasn't stabilized. Maybe Anivia decks go well against it but not enough of those on Ladder. Maybe the Ionia control decks can go well against it because they can Will or Stun the Sion. Maybe Freeze is better against this deck like a Sejuani Plunder deck or Ashe Noxus.
*The deck is also the type that would do better in an unrefined meta similar to Darkness (which has seen trending downwards slightly). Once meta stabilizes it will have more bad match ups to contend with.
Of course this is me just postulating, it's not set in stone yet. The deck definitely has high tier 1 capability and is in contention for best deck in the game. I think the smarter players might figure out some holes in the deck and target it for worlds.
