What's the context behind the Shen nerfs?

I love Shen, and will admit that I'm fairly biased towards him. However, looking over his current statistics, it's baffling as to why he's getting nerfed.

He has a ~49% win rate in every elo from Bronze to Diamond, with a 46% win rate in LCS, indicating that his overall power is not even above average.

He has a 10% pick rate , which is 11th among top laners (8 of which have a higher win rate than him), while he is a rarely picked jungle and support. He also has a 1-2% ban rate, indicating players do not find him problematic to play against.

His win rate among experienced players is around 53%, which puts him at decent, but nowhere near OP level compared to other champs. (Compare him to GP, who has a 56% win rate in experienced hands, and Wukong, who hits 56% at 15-50 games).

He has the same base health at level 1 as mini Gnar, and less than Sion, who intentionally is supposed to have low base health to balance his free health stacking.

He deals the least damage of any top laner right now (less than Warwick and Nunu top, who have abysmal win rates), which is fine, but indicates it's definitely not a case of "he's a fighter, so he shouldn't be super tanky if he's dealing plenty of damage".

It just seems weird that Riot would nerf a champion that's average or below average in multiple respects. The only reason I could possibly see his nerfs being valid is his high P/B in competitive, but even then I don't see how that nerf would affect his competitive, as Shen thrives as a low income, lane swap tank, so early game HP/5 isn't very important when he's in lane swaps and not dueling the enemy.

Stats taken from: http://champion.gg/champion/Shen/Top http://www.leagueofgraphs.com/champions/stats/shen