If your infrastructure is set up to unload X number of containers a day, and now you're dealing with ships carrying twice as many or three times as many containers then your unloading time doubles or triples. You may have been able to process seven ships per week. Now you can process only two or three.
If your infrastructure is set up to unload X number of containers a day, then you’re unloading X number of containers that day, whether it’s 100 containers per ship or 150. Except now you’re spending less time moving ships without unloading. So you’re unloading X number of containers plus Y number since your actual unloading time has gone up.
If the port had been able to process seven ships per week, and the ships are now carrying twice as many containers, then there’s no reason to assume you can now only handle three because you’re processing ships faster. So more likely it’s four ships which equal eight of the smaller ones.
And if your ships have doubled in capacity then shipping companies need send only half the number of vessels to carry the same cargo.
Unfortunately, the reality that is clearly visible off the coast of Southern California shows that your reasoning is completely invalid. There was no backlog of ships before COVID-19. Ship capacity hasn’t magically doubled or tripled in two years. And consumer demand has been way down due to the economic affects of the pandemic, so if anything shipping traffic has been reduced in the last two years.
Union issues mentioned another thread above is a much more likely cause than some imaginary lack of infrastructure improvement.