“They were designed to be entered one time, for the funeral of pharoah, and then sealed shut forever.”
Except there is no evidence that the pyramids at Giza were ever used for that purpose, nor that they were meant to be sealed forever.
Nor were slaves used to build them - those that worked on the complex were well paid, fed, and cared for - it was an honor to work on them. You cannot understand the complex if one thinks of it as a Christian, rather one must think like an Egyptian of the Old Kingdom, which means to think symbolically not logically; this is sort of like asking a aborigine hidden in the Amazon to understand social media, only that is an easier task.
Did you know that the interior of the Giza Pyramids reflect sound in perfect harmonics? Or that the whole Giza complex was designed as one structure?
While all the details you stated may be true; it does not alter the fact that the pyramids were NOT designed nor intended for the storage of grain or any other agricultural commodity. Which was the salient point of discussion. I also question the value of excellent acoustucs, to a mummy in a sealed sarcophigus.