If Riot starts to nerf mid champions because of an item again...
It will be ridiculous. I mean, Ahri was extremely OP after her rework, then she got nerfed. She had a pretty normal winrate after this until Luden's Echo came. It's not just Ahri. There is a lot of mid champion loves that item. It adds a lot of burst to champion.
They nerfed Syndra because of DFG, then removed it. See what happened. Now, if they nerf champions then nerf item I'm going to pretty sad to see this. I prefer nerfed item to over champions.
It became so popular on burst champions, even than Rabadon. Rabadon should have the most popular for AP - magical damage wise but it has been replaced by Luden's Echo.