I just played a game against a warwik, a yi and an ashe. My team was me a kayle (freshly nerfed and useless), the card guy and annie.
From the beginning of the game to the end, warwick killed each and every one of us in 1 shot. Even at full health, all of us dead in 1 shot. By one shot I mean that even if I invulned during infinite duress, his attacks were doing 150-230 dmg per hit at lvl 12 while mine did around 30.
Antistasis, that does not help explain anything. I have played against people far higher level than me in practice and won easily.
Warwick was doing this to EVERYONE. Me, twisted fate and anne all getting murdered in a few seconds regardless of items or defenses. Slow didn't slow him down at all, and everyone's damage against him was less than 80 per hit.
play many more games then return, it sounds like your just not used to someone getting an edge through superior farming and then using that edge along with a good setup and new players to completely make himself look OP.