I understand the point you're trying to make, but yes, these things usually do take time. In the examples you used:
Harbaugh - had Smith/Kaep in place and made the playoffs his first year (McD had Tyrod in place and went to the playoffs his first year)
Pederson - first season with Wentz Philly went 7-9 and missed the playoffs
Lynn - Has a future HOFer at QB so this is REALLY apples to oranges
McVay - Goff was already in LA for a year and got his rookie season out of the way
Nagy - Trubisky was already in Chicago for a year and got his rookie season out of the way
I think the true litmus test will be next season, when Allen has a year under his belt and has talent around him. Chicago having Robinson, Gabriel, Miller, Cohen, and Howard >>> what Allen has to work with. And then LA? Woods, Cooks, Cupp, Gurley... there's no comparison.