I agree that we will likely see regression from some of the players that you mentioned, along with less production from the DH spot. I also think it's possible, however, to see improvement out of the left field and 3rd base. I don't expect our offense to outscore our opponents by 100 runs or even by 50 runs. They might even fall to 5th in the league in scoring like the Blue Jays did, though I think that is very unlikely.
OTOH, our pitching should be much improved. We were terrible in our 4th and 5th spots last year. The ability of our starters to pitch deep should help the overall quality of our pen. I think that adds up to a net improvement, though I don't think that, in and of itself, is the whole story.
Some of our net improvement comes from the gains we made over the other teams in the division. While I don't think any of the teams will be pushovers, I do think that making improvements over them adds to our net improvement.