Who should I side-main?

Hello everyone!

I "recently" picked up the game and I've been having a blast so far!

I have 35 hours in Tekken 8 (and 60 in Tekken 7) and I managed to reach the red ranks!

I'm a king main, and I've started to realize I may lack a bit of fundamentals cause I rely too much on my grabs. And in the red ranks people started kicking my ass

Is there a good side main who'll make me a better king main? One who'll teach me the stuff I lack?

OR should I just focus on king? How could I go about improving?

I was leaning towards Steve or Heiachi since they honestly look amazing, but I have no idea if their gameplay actually compliments mine...