Your putting too much faith in the inspector.Good questions, I'm sure. But given that L&I [state AHJ] has been out and not red-tagged anything, I assume the best. There are Series labels on the cabinets; I don't if L&I required them. I know the SqD fused disconnect was purchased to fulfill the series coordination requirement.
They glance over the calcs the EOR or master (Administrator? they call it in WA?) signed and submitted for plan review (probably required a plan review on a 600 amp ) and see that someone calculated it, but they dont necessarily do more than that.
I know Square D QO breakrs have lots of documentation on the series rating combinations, but if the transformer numbers are correct, I seriously doubt any of that is needed as there is no way the fault current is very high at the disconnect.
The 600A disco could be for some other code purpose like the required outside main, or just so they could use 4 200A panels and call it a 600A service.