Lei Shen got full power of Ra and full power of Aman'thul - at least according to his story. He only died because Tol'virs used recalibrated Forge to wipe out all life near his current position. He was unmatched. So yes, he would beat LK 1 vs 1. He was also not succumbed to the curse of flesh so many LK attacks would simply not harm him.