“newer cargo ships—some launched recently—carry about 25-30% more cargo. Obviously, this takes 25-30% longer to unload.”
If you spend 25% more time to get 25% more cargo then this slows nothing down.
Larger ships could actually speed up unloading. There is less down time between ships. 1,000 containers is 1,000 containers. If they were all on one boat I think it would be faster than if they were on two boats because you would have to wait for one to pull away and the next one to dock.
I spent 30 years doing queuing analysis.
Your theory is linear thinking. That is not how queuing works.