Pretty much agree with all of this. Lots of guys had better offensive peaks. But Malkin, Thornton, etc were never close to the best defensive guys in the league. Datsyuk was. And yeah, arguably Zetterberg was better defensively, but he didn't play center as much as Datsyuk did.
Thornton is a great player, don't get me wrong. He had a lot more longevity than Datsyuk did. But at their peaks? It's not close. Datsyuk was a better goal scoring, in another tier defensively, and his impact on the game was much higher. He was always dangerous and forced opponents to play differently, and his hands were some of the best in the league, both in puck handling and vision. Was there a bump from Malkin and Crosby to Datsyuk offensively? Absolutely. But while Crosby was pretty good defensively, no other pure center really came close to the combination of offense and defense that Datsyuk had. Honestly it's a shame he only won 3 Selke's. He deserved a few more. Toews especially shouldn't have won it in 2012-13, and Kesler in 10-11 is pretty debatable too, but he didn't play the full season so somewhat understandable at least.
You know, I think there's some nuance to this.
Regarding his defense, imo Datsyuk was elite re: defensive transition in the neutral zone, to me he's the best player I've ever seen and probably ever will see in this respect. What I mean is when Datsyuk was on the ice it became MUCH harder for teams to get from their own blue line to the other blue line, and also Datsyuk would create a turnover in the Neutral Zone then immediately make a good pass, suddenly you're back in your own zone again but this time without any sort of warning. It's such a weird and oddly specific facet of the game that doesn't show up on the scoresheet and yet is so important, esp with regard to controlling overall play.
Among current players I really can only think of Marner and Stone that sort of have this same ability (might be forgetting some, if so apologies), but Datsyuk was so, so much better than both those guys at this defense / turnover creation through the defensive neutral zone.
Deep in his own zone? Imo he was very good but not elite. If I'm stuck hemmed in my own zone, I'd rather have Forsberg or Kopitar or ROR or probably even peak Jonathan Toews, Toews was once overrated but I feel like he's gone so far back the other way that ppl forget how defensively dominant he was in his prime. But counting the other 2/3s of the ice, Datsyuk was arguably the best player in his entire generation and maybe more.
All that to say Datsyuk was extremely good at the game called hockey, a bit tricky to explain to someone who's never seen him play. Glad we both had a chance to watch him in real-time (as did many people who are contributing in this thread)