Downloaded modernxp's MIDI pack. And it sure is 169k midi files just dumped into an archive, with no organization at all. When I have the folder I extracted it to open, explorer.exe uses 2.5GB of RAM and 25% of an 8-core CPU.
But you can avoid opening the folder by using Everything to search for .mid files! There's good stuff in here, but also a lot of ringtones, and newer MIDIs were apparently made by people unaware that there are instruments besides the default piano.
But you can avoid opening the folder by using Everything to search for .mid files! There's good stuff in here, but also a lot of ringtones, and newer MIDIs were apparently made by people unaware that there are instruments besides the default piano.