I'm not sure what more there is to discuss when a photograph is presented and you continue to say "it's just both players hand checking". No it's not, and there is crystal-clear, objective evidence of that. Parker is resting his left hand on Howard's sternum trying to create space; Howard has a handful of jersey, extended well away from the body, and in the process of grabbing the jersey is simultaneously preventing Parker from raising his left arm.
Could Parker have made a better effort to get to the ball? Only Parker knows that, but from my view, yeah probably. Does that mean no penalty occurred? Absolutely not. Are the players' respective actions equivalent, or just tit-for-tat hand-fighting? No, and we have demonstrable evidence of that.
What Howard did is a penalty, DPI or holding, take your pick. What Parker did is not a penalty; if he had grabbed a fistful of Howard's jersey or gave an obvious push-off with an extended arm, that'd be a different story - neither one happened.