The operations are the current r/w iops at time of the command execution. You can add a time value (eg 1s) after the command to have it refresh.
Looks like at that time the pool was busy with performing the backup.
Please note that due to copy on write the pool has to read a lot of data from the disks as well when re-writing data.
Have a look at your pool/fragmentation level; also your pool is quite full (84%) which is bad for performance as well, there is a chart somewhere that shows the performance impact of using up space; basically it says performance is best when used space <50%, don't go up over 70)
You could do your own backup (unless the camera software adds relevant information (i.e. this and that video is in this and that backup)
And yes, 11 TB usable, better (faster) to aim for 50-70% usage so lets say 20TB usable. Maybe add another 5T for backup delay.
50T raw if you do mirrors. Ideally write intensive drives (for duration not speed) , no need for extreme performance, but enterprise level drives of your preferred supplier, maybe 6x 8GB drives (depending on infrastructure & price sweet spot)
