FWIW: RAID 5 and 6 having problems is not a random hole you'll accidentally stumble into.

The man page for mkfs.btrfs says:

> Warning: RAID5/6 has known problems and should not be used in production.

When you actually tell it to use raid5 or raid6, mkfs.btrfs will also print a large warning:

> WARNING: RAID5/6 support has known problems is strongly discouraged to be used besides testing or evaluation.