For ability I'm fine putting Kopitar behind Datsyuk. At their best - I'd say Datsyuk is better. But for actual resume - Kopitar was more consistent in the playoffs.
Datsyuk's playoff resume is simply not that great tbh. He was nothing special in the 2002 cup win - just a rookie it's true, but he was also already 23 years old.
He was outstaged by Zetterbeg in 2008. He didn't do too well in 2009 - I know he had some injury troubles, but 9 points in 16 games is just not good - he was 10th in team scoring.
113 playoff points in 157 games - that's not even a 60 points pace per 82 games.
For what it's worth - Bergeon actually provided more offense in playoffs than Datsyuk. 62 point pace per 82 games.
Bergeron is better defensively than Datsyuk.
Bergeron in his playoff career averages 62 points per 82 games. Datsyuk is at 59 points per 82 games - which means Bergeron also outmatched him offensively.
There's the rationale.
I would argue the following:
Looking at career playoff performance is not relevant, considering that this is about PEAK, so 1-3 years.
Zetterberg outclassed him in 2009, sure, but offensively Bergerons best playoff series always saw him getting outclassed offensively by 1-3 other players on his own team as well (Krejci, Marchand, Pasta etc).
In my opinion, at Datsyuk's peak, he was 90% of Bergerons defensive skill (winning Selke's too), and 130%+ of Bergerons offensive prowess. He was another tier of player than Bergeron was at his peak.