[majkinetor]

> There is zero reason a process would have more than tiny slowdowns with even millions of files in a folder.

What kind of BS is this? Have you ever worked with one such folder? If you did, you would know that almost every app not doing some magic slows down to the point of being unsable (or even not working as described in original post). This is true for both Linux and Windows file systems.

[didgetmaster]

Exactly. Applications that are searching for files that have a certain extension (e.g. *.jpg) must read every directory entry and compare the file extension for that pattern. There is no magic call to the FS that says "Give me all the photos" or "Give me all the .jpg files). The application (including any command processors) have to do all that work manually.