I don't think he's a 'wasted' pick yet.. he has upside.
That said, he needs to come down with some of the deep balls and big plays. I wonder if he's got a little bit of a confidence issue right now, as it seems like he has missed more of the 50/50 opportunities (e.g., late game deep ball today) than he has made. Hopefully he can come down with a big play or two in the coming weeks and get his confidence up... if he held onto that deep ball late in the game today, that is a HUGE play.
It would've been a great catch, and it's not 'awful' that he didn't catch it... but, as @Smonroesaid, I bet Pittman would have come down with that... if Pierce is going to earn a big contract after his rookie deal, he's gotta make more of those tough plays than he misses.