Delpo's fitness was never a strength, he actually missed out on a chance to have a 2-Slam season in 2009 because of his horrible fitness in the RG semis vs Federer. For a guy as reliant on power as Del Potro, the wrist is all the more important. When he came back, he was mostly getting blown off the court by the top guys, he only really made it a contest with Nadal, who's a good matchup for him anyway. In 2009, he had a 5-5 record against Fed, Nadal and Djokovic (2-2 in Slams) and won a Slam as a 20yo, that is a pretty impressive record: surgery not only had physical effects but also derailed his momentum big time and made him lose a key development year. When he returned, he was pretty much back to the drawing board and took a relatively long time to get confidence back and power in his wrist. He also kept getting minor injuries afterwards, making the comeback even more difficult.
That's why I used 'surgical procedure' instead of surgery. I was quite young at the time and had no Internet access so couldn't really fully grasp what was going on, but I remember reading it wasn't an actual surgery but a minor procedure. Have tried to find out sometimes what it was actually, but to no avail.
It's irrelevant whether or not it was a strength. He was very mobile for a man of 198cm and if he wasn't, he'd never have been able to compete at the level he did. His movement made many shots possible that are now no longer possible. He moved particularly well out wide on the backhand and could solidly retrieve with interest going cross court. Now that his fitness has dropped (I'm talking agility, flexibility and his CV is alarmingly poor) he is unable to make balls that he did in the past and going 2 hours plus into a match shouldn't be a problem for a 24 year old tennis player, but as a result of his CV endurance, the rest of his physical attributes deteriorate and he is reliant on pure ball striking which makes him vulnerable to both attacking players and players who are defensively strong.
And the time off perhaps derailed progress, not necessarily the surgery itself. And power does not come from the wrist at all. If his wrist hadn't healed 100% there was no way Del Potro was stepping back onto court like he did early in 2010.
Yes, and why do you think he kept getting injured? His fitness levels were and seemingly from what I've seen are still not what they were in 2009 making him far more susceptible to injury, on top of the fact that he was always going to be susceptible to injury being a tall man with long levers.
There was a lot of talk and 95% of it was false. Safin never received any surgical treatment whatsoever. The only procedure he endured was rehabilitation as it turned out to be chronic tendinitis of the right knee. Afterwards he was a shadow of his former self and could barely move to the forehand wing (amongst other problems).