I don't know enough about their app to give a detailed response, but it seems like the optimizations they performed could have just as well been applied to their HTML5 version. WebWorkers, for example, are available on iOS.
It could be that they could never get true native speed without writing it natively. However, in my experience their HTML version was so awful that I suspect a lot of it was from bad decisions on how to use HTML5. That may be the problem though: that it takes deep knowledge to know how to leverage it correctly and speedily.
It could be that they could never get true native speed without writing it natively. However, in my experience their HTML version was so awful that I suspect a lot of it was from bad decisions on how to use HTML5. That may be the problem though: that it takes deep knowledge to know how to leverage it correctly and speedily.