@sjw @shibao @EdBoatConnoisseur
Had to check wikipedia:
RAID0 → All in serial
RAID1 → Mirroring, 2+ disks
RAID 2-4 → Single-copy Parity
RAID6 → Double-copy Parity
RAID7 → Triple-copy Parity

How is using RAID $number clearer?

Specially as then it goes really messy when you need to describe nesting precisely as RAID1 is 2+ disks.
Like RAID1+0 vs. RAID0+1 is horribly unclear compared to just saying (here for 6 disks): 2 mirrors, 3 (disks) each or 3 mirrors, 2 (disks) each.

And idle/hotswap disks also aren't in the picture of RAID.