As I understand it crossbridge just produces bytecode. So there is nothing about it that is fundamentally better than coding in ActionScript. It might be faster, as e.g. the compiler is better. It might be slower as a project abandoned by Adobe years ago, that has seen little improvement since. It probably depends a lot on the code in question.
I’ve written pathfinding code in ActionScript, and it is quite up to it. And this was a few years ago when the computers it was running on were much slower, and certain aspects of the Flash runtime where much more of a bottleneck than now. Hard to say whether that is true in your case, but you might be suprised what it is capable of.