Leafs are always going to be a high-event team so absolute shots on goals won't change even if we added in a #1D, IMO. That's not really a favourable metric to look at. That's just how hockey is played in this era.
As for Polak, he had his flaws, but he was fine in the bottom pairing role. Every team wants to perpetually upgrade their bottom-pairing D, for the most part. He was physical, and it was a nice bonus to have in the playoffs. He also cleared the front of the net decently. He just had terrible gap control and an awful stick. And like you said, couldn't exit the zone very well.
The bigger problem to me, when it mattered, is having Hainsey eating up heavy minutes on your top-pairing- playing against top lines regularly, and who can't exit his end of the ice effectively. We also need a guy who can eat those PK minutes, and Hainsey would be fine as a supplement to that on a bottom-pairing spot. That's who we need to move down the lineup. A guy who is playing above his slot at a premium position, who we'll need to replace eventually.
As for Polak- I'm not going to pick on the bottom-pairing, 4th line guys too much in the cap era as long as they can do their job relatively effectively. He was a convenient scapegoat because he wasn't very good at times, but the last 2 years, I thought he performed admirably in a bottom-pairing role when it mattered. My opinion is Hainsey was one of the two players that got exposed the most last year when it mattered.