The meta of this game is mixing up your opponent, preferably with a 50/50. Also, you said that it's a problem with the variration - pick another variation, that's what they're available for. I know Kotal just generally struggles against zoners, and a parry buff could help fix him, but you just need to learn to deal with certain matchups and tactics. For example, I would NEVER pick Brawler Cassie Cage against Grand Master Sub Zero, I would pick Spec Ops.
The only buff that is needed is some tweaks on his parry because it's not great or particularly practical in most situations.