First of all, you have a chicken and egg issue - teams built around Kopitar are not going to be high-scoring teams because the team's top center is not a run and gun player. Comparing stat totals is silly? There's not much else, except advanced stats, which are not terribly kind to him either. He's where offensive chances go to die these days, especially on the PP, and he's a big part of the reason the PP is as bad as it is; it ain't the coaches. I don't care how much lipstick you put on that pig, six PP goals for your top center who gets top PP minutes is abysmal. He's still elite defensively, but he's mediocre offensively. Gifted offensive forwards are more rare, and therefore more valuable, than defensive ones. Being a top offensive player without providing much defense still makes the forward elite; the opposite is just not the case.
Kopitar used to be in the conversation as one of the league's top ten centers, he's just not one of them anymore. You don't need anything besides eyeballs to see that he is not what he once was in the offensive zone; not close. He's a high-end Michael Handzus now. Don't get me wrong, Michael Handzus was a terrific player in his own right, but he was not one of the best players in the league. Neither is Kopitar. He wouldn't be the top center on a lot of teams in this league, and would not even be the second line center or several.