>So, for open-source, ZoL is the 'mainstream' ZFS.

Wrong, there is no ZoL anymore "just" OpenZFS:

https://openzfs.org/wiki/Main_Page

>>The OpenZFS project brings together developers from the Linux, FreeBSD, illumos, MacOS, and Windows platforms. OpenZFS is supported by a wide range of companies.

And again ZFS is NOT part of Linux.