Yea, Malkin going to Montreal would have helped the Canadians a lot more than Weber. I'm sure GM Bergeron didn't want the Eastern Conference Pens coming into Montreal twice a year with Subban and the fans seeing Montreal behind the Pens in the wild card race. He seemed like he "had" to trade Subban to the Western Conference, instead of making a better trade with the Pens as you suggest.

I'd rather have Malkin every day of the week.

I would too, but this was just a hypothetical trade. Centre > D