I thought they would miss him from the outset. He's definitely impacted the offense as it wasn't a great hitting team with him anyway.
Pitching is obviously important, but I saw no real need to get Lester. They already got Shark and had a good staff. Ultimately, they're fortunate they've pulled themselves together and it looks like they'll make the postseason, but everyone knows you have to score runs to win and Oakland has made themselves look especially vulnerable in that department.