Berdych is much better at the net, he's actually not afraid to come in and put volleys away, that's one of the primary reasons why he's so tough for Noserer - Del Potro is a baseline camper who won't approach the net even after he gains advantage from the back.
Also you're confusing mental strength and technical ability. When Berdshit shows up, he's a clown for sure. At his best his BH >>>> Del Potro.
Del Potro approaches the net less often, but when he does he usually has good numbers there. Berdych can volley excellently at times, but he's very prone to break down under pressure, see his volleying vs Nadal at the AO this year.
Berdych on his best days has a better BH than Del Potro - JMDP's backhand is mostly a safe/set up shot, he doesn't take too many risks with it but hardly any errors too. But as far as consistency is concerned, JMDP wins by a landslide. At his best, Berdych is as good or better than Del Potro for sure, but on average it's a clear edge for Delpo, which is why he's the far better player. Even while injured/playing horribly, JMDP would never lose in a big tournament to the likes of Darcis or Gulbis, it takes a top seed to take him out.
Maybe something like Paris indoors or Shanghai
Definitely. He should also win one of the clay masters at some point, he plays his best tennis on clay. Point is it is extremely unlikely he will retire with 0 Masters.
Context is important as well. Nadal was injuried and Noserer choked. It was not as impressive of a run as it looks on paper.
The draw was full of players who could have taken advantage of that, yet it was Del Potro who did. Nadal wasn't at his best, but was still too much for the rest of the field. Beating Nadal and Federer is impressive no matter the circumstances.
It doesn't matter, his H2H vs the big 3 is embarrassing: 7-26, doesn't matter if he can trouble them or not. It's still a joke, my bich comment stands.
That only proves that the big 3 have been better players than him over the years, which is not very debatable, everyone knows it. If he was their bitch though, he'd not have taken out in important tournaments. He was the only man other than Nadal to beat Federer in a Slam final, gave Nadal one of his worst beating in GS and reduced Djokovic to tears after he failed to get an Olympic medal.
In tennis terms, a bitch would be someone who does not represent a threat in big matches, JMDP does not match that description at all.
David is more consistent, he's been a top 5 player for a long time and usually has less embarrassing losses.
Are we talking about the same guy who has losses to Bellucci and Istomin this year, and even in his best players has Slam losses to the likes of Verdasco, Melzer, Ramirez Hidalgo and co.? Del Potro is far less likely to lose to low ranked players.