The biggest problem with cocos2d now is that SpriteKit is slowly making it irrelevant, at least for iOS-exclusive apps. Apple basically ripped it off and remade it and packaged it with iOS. It even has the same mode/scene structure! Cocos2d has almost nothing that SpriteKit doesn't except for being open source and a few extensions.
Why would I use cocos2d with swift when SpriteKit has such close integration with it already? There's still a place for cocos2d, but with cocos2d-X, the C++ cross-platform version.
Don't get me wrong. SpriteKit is great place to get started, but when you need something more powerful, that is where Cocos2D comes in.
which suggests Swift isn't actually more performant than ObjC.