The problem with talking about Hakan's stats before-and-after Ibra is that he was constantly played out-of-position before Ibra came.
He's played without Ibra this season and still done very well, so there's that.
I think De Bruyne is better than Hakan, but I'd say that De Bruyne is the best in the world in his position. Others are Muller, Bruno, Havertz (not this season), but those are the only ones who I think are in his bracket.
I'd personally put Hakan as second behind De Bruyne, penalties are not easy, but, I also think that his penalties over-state his importance. He's a good player, but Hakan is better. Muller does the second-striker/CAM thing better than Hakan, he scores more, but Hakan is a better passer and holds onto the ball better, distributes it better, makes his team tick.
Yusuf Yazici is also pretty good in the attacking midfielder role.