i wouldnt call it a massive improvement. do you remember the eagles game? or the broncos game? or the seahawks game?
sure they looked fine against inept offenses like the browns and steelers and bears. but they got absolutely worked in a lot of those games in the second of the season.
the lions seemed like a "try hard" team last year (which campbell and co deserve a ton of credit for), but i dont know how well that will translate in the future.
otoh, theyre not done yet in free agency or the draft, and i think this is a recognition by the front office that they still have a long way to go before they start competing.