I have the same storage strategy as you. SSD stores html, config, db.. and HDD stores userfiles. However, you can try comparing it to SFTP.
On my server, SFTP loads faster with almost no latency, while filerun via webdav loads a large number of files will be frozen for a few seconds
the thumbnails was stored at .filerun.thumbnails which was a hidden folder
Yes，just loading files list is slow. both on web page and webdav client.
When I click on a folder on a web page, the screen goes blank, and it takes five or six seconds for the file to load.
I'm sure it's not because of the network, because it's over a gigabit LAN, and there's no problem with opening folders with fewer files
Customer support service by UserEcho