According to the Rankeds data by the Lead Gameplay Designer for League (@RiotPhroxzon) the winrate of Atakhan is 78.9% along with the First Turret Winrate with 70.4%. 

Should be interesting to get the comparative data with the winrate after getting Atakhan after going 1 or 2 k gold below, and also check the difference of winrate between the two Atakhan.

I think you can be behind even if you don't have the bonuses and thanks to the Atakhan Mechanic win games. Specially to the GA Atakhan Mechanic.

This @LFLOfficiel (LFL2) game is one of the best examples 👇