Thanks @renomarx for sharing this information. I’m glad you’ve found a way around this. I have to agree with @weikai though; this problem is more complicated than it looks.
In my case, I have moved the MySQL server from a Docker container to my localhost, which is also ext4, and it was still slow. But hosting the application locally in stead of in docker - while using that same local MySQL server - improves the speed more than drastically.
Unintuitively, It seems that this is not Docker-specific volume/mount/link/share/volume related, but Docker related nontheless.