If you request a file with it's fully qualified path name (FQPN) like /var/www/html/wp-content/uploads/2018/11/full-filename.jpg does the OS (be it Linux/Unix/Windows) and/or PHP perform any kind of "search" for the file or does the FQPN allow the file to be accessed directly?
What I'm trying to figure out is this -- If I have a folder with 10,000 files in it, and I request a file within that folder using its FQPN, is the retrieval of that file any slower than if it was requested from a folder that has only 10 files in it? Does the fact that the folder has 10,000 files in it have any impact on the speed of the file retrieval?
The query not different between file and folder, and sure 10 files fast then 10,000 files. So you need to keep the appropriate number at each layer, like 1,000 * 1,000 * 1,000 and not like 10 * 100,000 * 100. For today's computers, everyone can't feel quickly less than 10,000, but you're right, we can't just give up thinking about it.