You could answer yes to both questions. More defensive responsibility could make it harder for Yzerman to reach 155 points. Very few Selke trophy winners have finished top 5 in scoring. I know that we're not necessarily talking about Selkes but being a good two-way center in general. However, it's a fair point to make. And Malkin would certainly have scored more points if he played in the 80's. Just like Gretzky would not score 200 points in today's NHL.
I'm not holding Malkin to a higher standard. My point is that Malkin at no point in his career has been considered a solid two-way player. For that reason, I'd rank not only Yzerman and Sakic, but also other centers in the same tier like Trottier and Messier over him. Players like Lemieux or Gretzky are also not great two-way players, but their offensive peak pushes them way beyond the Yzermans of hockey. Malkin is not that great offensively that I can ignore the other side of his game completely. We're not comparing him to Carbonneau or Bergeron here. Yzerman and Sakic were terrific offensive players themselves. If he's better than them offensively, it's not by much.
Also, let's not forget that Yzerman and Sakic are two of the best leaders ever to play the game. While that's hard to measure unless you're in the locker room, I've never heard of Malkin being mentioned as one of the game's great leaders.
We'll have to agree to disagree, but to me, ranking Malkin ahead of Sakic and Yzerman ignores the two-way game and intangibles and makes him into a Jagr or Lemieux like offensive force, where we can just overlook anything but offense. I don't see him on that pedestal.