In my opinion, not everybody who fought against said characters should scale. (I mean, like every single person who fought against Scorpion should be on his level) At least on Scorpion's case, since it is pretty clear that his power grown since previous incarnations.
On all Mortal Kombats except for X, Scorpion usually got beaten on most of his fights. He gave problems and won against a good lot of people, indeed, but he lost more than he won. On MKX, Scorpion becomes more controlled, resumes training, and he is suddenly kicking the ass of four powerful characters on a row (The first three - Johnny, Cassie and Sonya - while restricting himself to not kill/harm them seriously), before temporarily fighting Shinnok, and only THEN losing. And there's also that he beaten bloodlusted Raiden, and was ready to kill him.
So, MKX Sub-Zero may scale to him, but any other versions were weaker than his MKX form, and stronger than his previous form.
If that's confusing, I'd put this on a chart quite simply: MKX Scorpion > MKX Sub-Zero > Kuai Liang > Scorpion > Bi-Han.
