I am currently working in Unity 3D for a 3D game in a 4-person team. My core business is education apps, for which I use both C2 and C3. For my purposes, HTML5 is the most important technology, so Corona would be a huge step backward in terms of usability and deployability. We looked at Corona a years ago, but chose Construct 2 when we realized that we could entirely skip the app store approval process with HTML5.
In the end, C2 was the best choice for HTML5. After 4 years with C2, I don’t think there would be any benefit to using Unity or Corona for 2D development. I haven’t run into performance issues that I couldn’t solve for mobile, and deployment through something other than a website would be a huge step backward in our target market (schools) - most schools in the US use chrome books, and creating apps that only work on phones would cut out most of our users.