Pinning ability can literally make or break a Reinhardt. The only times you should charge are when you know your target won't escape and you know you won't miss. Plus, he was easily singled out from his remaining teammates. If he was a good Reinhardt, he would have taken the opportunity to shield, back off, and regroup with his team since it was only a Zenyatta attacking him. Instead, he missed his pin twice, leaving himself open, boxed himself into a corner, and practically handed Zenyatta that kill. Even if Zenyatta followed him outside, at least his team could have reached him.