Have you seen how he crashed Nalbandian and Ancic a day before he lost to Federer and Nalbandian? IMO Federer and Nalbanian are really wise and found a way to humiliate Del Potro who has really one-sided tennis but I have to admit well rounded.
I see your point- but I still don't think he was playing in top form at those tournaments. Ymmv. But yes- they did not let him get any sort of rhythm. To start to try to make inroads on the top players- he needs to come in more when he has the opportunity. And drop shots will always be a danger- as Nalby was quick to exploit. Delpo does have some big limits on his game right now (movement forward and back, tendency to stay back for too long, a weak second serve, etc.) but I think he is capable of building on it. If not- I will be disappointed.