shouldnt this have the storage space of 1 drive with 3 redundant copies?
The default for RAID1 would be 2 copies. Unless you select the c3 flavor of RAID1 I think this view is correct.
Btrfs’s raid1 differs from raid1 (where all drives are mirrored). Raid1 means data is written in two redundant places, raid1c3 means three and raid1c4.
So it’s good feature but named after non-related system