User blog comment:ToastSoul/Cape Kaga/@comment-200.128.77.250-20160503122646/@comment-177.159.52.149-20160503181506

OP here! I did some research and from what little comes up, it seems there's no real difference between わけがない and はずがない (sources 1 2 3 ). That said, I'm no native speaker of either english nor japanese so I leave it in your hands.

One last thing, you might want to change the 鎧袖一触 line to "It would be an easy win" or something along those lines, though that could just be me wanting everything spelled out.