Against characters with small hitboxes like Johnny Cage I like to use my D4 like it's a F4. Maybe try D4 OH smash/gotcha grab mixups. 2 1 is 15 frames and hits crouch blocking opponents, so if they just sit and crouch block (which they probably will) try that.
Jax can Zone johnny Cage out pretty well and punish reckless dashing with F4 projectile into pressure or F4 OH splat ex ground pound for 26%. The best way to play Jax is to be unpredictable, use your stagger strings and don't be afraid to D4 or Grab a lot. He's a very fundamental heavy character, he'll help you understand the game.
