Lazor called a very different style offense down the stretch, with the QB under center a lot. Nagy is taking the reins back. Everyone talks about the cake schedule but the OC was a bigger factor IMO.
Besides Tarik being back for third down duty, they have a very capable third RB (Damien Williams) and invested a 6th rounder in Herbert. Montgomery needs volume to be a top 20 back. I don't see a lot of paths to that, presuming Tarik is the same guy he was 2017-19 (53, 71, 79 receptions.)
I expect them to move on to Fields early - they have a late bye this year, so looking at possibly entry points the Detroit (H) - LV (A) games seem like good first starts. Think about how the season might play out for Nagy/Pace, who are fighting for their jobs: they'll get blown by the Rams WK 1, have a potential shootout game versus the Bengals, and travel to the Browns. At 0-3 or 1-2 the pressure will be on.
Fields will be taking off instead of checking down, and he'll vulture some TDs. Robinson has never played with a QB and Mooney will see more accurate deep balls than he will from Dalton. I could see the offense beginning to click under the rookie, but I don't think it will be because of Montgomery.