Well. In Diamond and above, she has the 2nd highest winrate right behind Nidalee. The problem is that she shot up over 10% overnight with the buffs she received to her E. That IS significant and you wouldn't really expect a champion to rise that high with someone with a more complicated kit than say Galio or Warwick who have some of the highest spots in Champion.gg. They both drop in winrate the higher you climb in ELO/Rank whereas Nidalee and Elise rise and there is something to be said about that.
Now looking at some of the statistics. Galio, Heimer, and Trundle(support) have ~1% or less playrates. You really can't make a judgement call on whether they are OP or not based on a small sample size as such low playrates would imply that "mains" are playing them, or that they are being played almost exclusively into heavily favorable matchups. When champions, such as Elise or Nidalee just get picked into ANY matchup by ANY (higher skill) player and still thrive with 55+% winrates, one should suspect that they are exceptionally strong right now.
I want Elise to be strong, but I think she is too strong right now. The 1.6 stun duration at level 1 is higher than it has EVER been. The last time Elise was called OP, it was when she had a 1.5 second stun at all levels (there were other reasons she was strong, but there is a reason it was lowered to 1 second at level 1). This change to her E was too much in conjunction with all the other buffs she had received since season 5.
There is an interesting statistic that I found when Elise was weaker 2-3 patches ago. Less than 20% of players used the maxing skill order Q-->E-->W; however, there was an increase of over 5% in winrate amongst players who did so. This I think is significant. When 70-80% of players were maxing Q-->W-->E, they were missing out on a lot of the power that came with leveling E which included a longer stun on a lower CD, more Rappels, and more recently, bonus damage to Spiderlings that scaled with rank when using Spider E. What you got with leveling W first was just more damage and a little bit more sustain. The bonus damage situationally in spiderform from each skill if you maxed W or E was relatively similar as the 140% Attack speed versus 100% bonus sustain and damage from spiderlings is close enough that really all you gain from W max second is the burst damage from human W.
What does this mean? Well, she was in a spot where she was better off building off-tanky (penetration and tank) and being a stunbot mid-lategame, but many people were not optimizing to this playstyle. Right now, she is best with a early to midgame burst assassin, which honestly, I like a lot better, but she is able to do that because she has such a strong stun without having to invest in it. She has too much power in the rest of her kit to allow her to have such a high duration stun at level 1. If they are to keep her level 1 stun duration high, there need to be cuts in the power of her Q. I personally would rather have her stun duration lowered, but I'm not sure that is going to be implemented immediately. We'll see what happens, but I do believe she is a problem right now. Peace.