He listed Dustin Brown because Dustin Brown is a forward who Kopitar played the vast majority of his time in the NHL with, and Drew Doughty is a two-way defenseman who had one 60-point season in his career. Doughty is great, but offensively he isn't exactly Bobby Orr.
Look, I’m not saying Kopitar is better than Malkin, not by any stretch, but people can't just blindly point at offensive production between the two while ignoring the vast differences in the situations the players were in, and also ignoring the defensive side of the rink.
What are the statistics like if the players had been drafted by the opposite teams? Do you really think Malkin is leading the league in scoring playing with Dustin Brown and Justin Williams, in a defensive-oriented system, with much less talent on special teams, while also being the focal point of the other team's defensive efforts for his entire career?
Malkin was the better player, but I don't think the gap is big enough to change the levels of success each had when it comes to Stanley Cups, assuming everything else was the same. The Kings would still have won Cups with a trio of Malkin, Doughty, and Quick, and the Penguins would still have won with Kopitar being a dominant two-way center behind Crosby.