I don't see any universe in which a 29 year-old Archer and a 38 year-old Lackey are remotely comparable, or where 3-year averages are a good way to measure a 38 year-old pitcher's projectability. Archer is a very good pitcher, probably a legit #2, and Lackey is pretty much done.
But that's not the issue. The issue is cost, and Archer - as a very good pitcher and cheap, is somebody the Rays would have to be blown away by an offer to deal. I don't think that's in the best interests of the Cubs.