Fedorov burst into the league as a youngster because we had a weak team and he was afforded a lot of ice-time. Datsyuk was a late bloomer because we had a power house team and he mostly played on the 4th line with not much PP time
Whilst I cannot dispute that the rookie Fedorov had less in front of him (Yzerman) than the rookie Datsyuk (Yzerman, Fedorov, Larionov, even Draper) that misses the point. Fedorov at 21 was a FAR better player than Datsyuk. The only reason Sergei wasn't in the NHL at 18 or 19 was because of the Iron Curtain, also the reason he was a 4th round pick and not a top-5 pick as his talent deserved. He scored 79 points his rookie year - roster depth and higher scoring era notwithstanding, it took Pavel till his 5th season in the NHL to top that. There's nothing wrong per se with being a late bloomer, most players are, its usually only lottery picks like Crosby, Malkin etc who can come in at 18 or 19 and perform like stars.
When Pavel arrived, he was a shy, undersized kid - outstanding stickhandling ability that had everyones eyes popping out, but no-one, no-one predicted the 2-way beast he would become. How much of that was opportunity, maturity, increasing strength, confidence, desire, Babcock's coaching, who knows? The fact is Pavel was 27 before he had a season that could be compared to Sergei. At 27 Feds had won 2 Selke's, a Hart and was a 3-time All-Star.
Fedorov was bigger, stronger, faster, had a better slap-shot, a better one-timer, as good defensively and almost as good a stickhandler (but no-one compares to Pav). Oh, and 163 points in 162 playoff games going head to head against the likes of Sakic, Forsberg, Modano, Niewendyk, Roy and Belfour year in and year out throughout the Dead Puck era.