Jax is fine the way he is. No need for any buffs or nerfs, in my opinion but for the moment I exclusively play Grinnin' Barrett. I can't speak on behalf of the command grab variant.
The only issue is that 22 is supposed to be a high, mid. But as it stands it's actually high, high. It's only purpose right now is to punish, which is a fine purpose!! - it's not in need of a buff at the moment. He has other punishers like 1~DB4 or 3~DB4. 3 is the optimal damage punish button, I believe, giving 299 damage for a bar over 2,2 which gives 288 (I think). 1 is obviously for tight punishes and 3 for super large punishes and 2 for when you can't punish with 3. Each has their moment to use them, yknow.
Even at that, F3 is 9f and by punishing stuff with that you can achieve 295 for a bar so it's like, might as well use that most of the time for the perfect mix of speed, damage and hit confirmation in the event that you miss the punish.
EDIT: I'm seeing a lot of request for B32 to be special cancellable. That'd be too strong, it's already a -7 low option. If you want damage and to keep them in the corner you need to guess and go B3~DB4. DB4 is also -7 but it's got a massive gap that anybody can full combo punish interrupt with most buttons. The move is fine the way it is.