But using that pricing, 24TB with Jottacloud would be 450 EUR/year, which is still on the order of $1000. The larger point is that disk sizes are always growing, and while 24TB may seem unnecessary to you, it's very easy to build an array that is cumbersome to backup. And IME this has remained true for the past two decades.
You're right that the cost effective way of performing large backups seems to be just buying another array and hosting it somewhere offsite. But that still doubles your array cost, and so is not something to be done lightly.
FWIW personal users want availability too, unless rebuilding arrays from scratch is your hobby. A simple mirror is a form a raid, which you can only get away with if your storage requirements can be taken care of by a single spindle. If that's where you are, fantastic. But that doesn't describe most home ZFS users.
So for 24TB you would use two accounts, assuming they're fine with that, and your uploads would run at 5Mbps per thread, with 12 threads in parallel.
That will let you upload 100GB every 4 hours, which should be enough. And the total cost would be 180EUR/year, which is pretty far from $1000.
If I had an amount of 24 TB to back up I'd buy my own server and harddisks, and I'd physically set that server up at work or at home. Then, travel to the data center (I live in Amsterdam Area, so enough choice) and put the server there, again, physically. No need to "upload 24 TB".
RAIDZ et al. is about availability. Which makes sense for businesses, but for personal data an offsite backup makes more sense. I'd just go with a mirror of 2 different disks, with different serial numbers (ie. different orders).