Nobody is writing him off. However, he should be tearing it up now...
Not really. Based on what exactly? His showing at Wimbledon last year?
His game has a lot of room for development. As it stands, his lack of outright weaponry and propensity for tactical tennis means he has to be mentally sharp for every match he plays. Unfortunately, however, he's obviously in a very poor state of mind right now as the weighing pressure and taxing circuit grind him down. And as he loses that edge, the more experienced or physical players are able to put a lot of matches in their hands simply by making him stay out there. He's inexperienced and underdeveloped, so there's nothing to suggest he should be lighting anything up right now, but he has plenty of time and potential to grow.
You might not be writing him off, but you might as well be to blatantly undermine everything in play right now.