Honestly, if it’s important enough to RAID, it’s important enough to do right and run full fat ZFS.
You could also go the mdadm route with individual disks but ZFS pools are so battle-tested that whatever unholy edgecase you manage to create will almost certainly be something someone has encountered before, and it’s probably well documented somewhere how to recover from
So one should use ext4 for RAID 5&6?
Honestly, if it’s important enough to RAID, it’s important enough to do right and run full fat ZFS.
You could also go the mdadm route with individual disks but ZFS pools are so battle-tested that whatever unholy edgecase you manage to create will almost certainly be something someone has encountered before, and it’s probably well documented somewhere how to recover from