Kung Lao defeated the Deadly Alliance in MK9 whereas Liu Kang was murdered by them. You could try to say that Liu Kang is stronger because he defeated Shao Kahn and Shao Kahn killed Kung Lao. However Shao Kahn was also killed by the Deadly Alliance and you could say that Kung Lao was only killed by Shao Kahn because of a sneak attack. You might also try to use that same logic as the only reason why Liu Kang was killed by the Deadly Alliance. However Raiden was also defeated by the Deadly Alliance in the Mortal Kombat Deception intro. And he killed Liu Kang on accident.