Looking at the entire year, I would say he certainly was the better goalie. He was tremendous down the stretch and if he didn't play so well in Miller's absence the team could have missed the playoffs.
On the flip side, Miller played well out of the gate, while Lack had a bit of a slow start. Miller helped build the cushion in the standings, which contributed to making the playoffs.
IMO the team needed both of these things to happen to squeak in, yet a lot of people talk like they would have made it without Miller. You just can't pro-rate Lack's .921SV% over an entire season and say they would have been the better team had Miller not been signed - that's not how things work...
Miller wasn't good to start the year either, the Canucks PP was. Miller posted poor numbers for a while, and they only became nearly average by December when he had a very hot stretch. IIRC, and opendoor or someone else could probably back that up.
Eddie Lack started rough because he was getting infrequent games. He came into the season looking tremendous through preseason, ready to be at least a 1B, but this team decided it didn't want a goalie controversy and kept the hungry young goalie down.
It's a pretty frustrating situation all around, because like afool mentioned above, they certainly don't see Lack as an option here. They felt the need to bring Miller back into the fold, meanwhile we hear this week he won't be healthy until late July. If the plan is to make the playoffs every year for the next 5 years, Lack should be the goalie you go with, so I can't really understand the logic of moving other than the hopeful 2nd rounder we can get, and I hate that rationale.