I disagree completely here. Del Potro's problem has never been UEs. Unlike Berdych and Soderling, he plays high % big hitting, hitting hard down the middle until getting a short ball to put away. This is enough to dominate low ranked players easily (unlike Berdych and Soderling who are often victim to shock losses), but his problem against the top players has often been not taking enough risks, playing it too safe. He was far more aggressive this week, more than he had ever been since his comeback. UEs have never been a problem. His serve, yes, it's poor for a big man and needs to keep improving.
His injury isn't blamed for his current losses, but for stunting his development; I'm afraid he can never get back the years he lost, although he's still young and can have a great career regardless.
How can you say he doesn't have a problem when he serves first in a 17-19 lost third set without generating a single matchpoint?
It was pathetic to watch Federer block and slice to the middle of the court and while Del Potro punished him sometimes he missed just as much. That's not a sign of a player in control.
Many games Federers serve was clicking and Delpo UEed so badly Fed could hold easily with 2nd serves and rally shots to the middle. It was honestly kinda pathetic for long stretches.
Del Potro needs to understand that when a top player goes defensive vs him it's more important to not gift away points than to hit winners. Federer, Murray, Nadal, Djokovic are all way to secure to gift him right back if he keeps wasting chances.
The entire 3rd set by Del Potro was a big wasted chance and not because of Federers high level but because Del Potro himself couldn't play with the margins to put pressure on Federer. He served first for gods sake and yet failed to apply pressure because of his errors and wild chance shots. Only time it worked was when Federer served for the match and then for once he could string together a few good shots.
But I honestly lost count on how many 2nd serves and short balls Del Potro just whacked in the net or out. If you serve first in a 3rd set, lose it 17-19 and didn't generate a single matchpoint then you got a big problem stringing together points.