I am definitely open to considering that Marty Barry was underrated in the HOH Top Centers project, but I have no idea why we would bring Stastny into the argument. It would be one thing if Stastny and Datsyuk played in the same era and it was clear Stastny was the better player, but that's just not the case, you're just bringing in a random 3rd player from an era that neither of these two played in. If Barry was underrated in the project then what's to say that Stastny wasn't overrated? Also, in Stastny's case, he had at least one prime/peak year pre-NHL, and played in a very defensive division, 2 factors that likely affect his vs.X score.
This is all secondary though, Stastny really has no part in the discussion, a much better approach would be to just compare Barry and Datsyuk directly...
7yr vs.X
Barry: 89.6
Datsyuk: 82.5
This is a difference of about 7 percentage points...to put that in perspective, in this year's NHL that is worth about 6.32 points over an entire season. IMO Datsyuk's elite defensive play every game is more valuable than 6 points of extra offense over 82 games. Datsyuk also has a stronger Hart and AS record than Barry. Therefore, as far as regular season goes, I would give Datsyuk an edge.
Barry was a great playoff performer, and better than Datsyuk, but Datsyuk is a very good big game performer in his own right (although not on the level of Barry). See this from Datsyuk's bio:
Prime Playoffs (’04-’15): 127 GP – 39 G – 68 A – 107 Pts +34
Olympics (’02,’06,’10,’14): 23 GP – 5 G – 15 A – 20 Pts +17
Remember that in addition to the above offensive numbers Datsyuk is also playing elite level defense in the playoffs.
So Datsyuk has the edge in the regular season, Barry has the edge in the playoffs. I cannot agree that your claim that Barry is "most certainly better than Datsyuk" is accurate, as a fair argument can be made that Datsyuk is the better player.
If someone wants to say the two are close, I am fine with that; however,with regards to the series, please remember that we are comparing Chicago's 2nd line center with West Lafayette's 1st line center.