I think the debugging experience is the same as just about any other platform that I've worked on. It's not significantly better or worse (I work mostly in C++/VS/Win have recently started work on a mobile project that required me to get acquainted with Xcode).

I'm comfortable with Objective C but I can certainly see the allure of Swift. Having said that, I'll bet that it's less XCode/Swift that is preventing newcomers from iterating quickly as much as the platform itself. Rather than really learn the platform, quite a few devs seem content treating it like browser and leaning on a webview.

I'm thrilled to see where React Native takes us but something tells me I'd have a hard time getting it past the lawyers based on some of the licensing comments I've read here.