And in your particular situation, 3 refurbished WUH721414ALE6L4 are the same total price. If you put those in RAIDZ1 then that's 28TB with about as much reliability as you can hope to have in a single device. (With backups still being important but that's a separate topic.)
What do you mean by cycle?
The amount of time they stay on a single drive.
Note, disk failure rates and raid or similar solutions should be used when establishing an availability target, not for protecting against data loss. If data loss is a concern, the approach should be to use back ups.
But yes, I've done the math. I'm just going with the BB numbers here, and after a few years it adds up. The way I understand "peace of mind", you can't have it with a single drive. Nice and simple.
Whether that's right or wrong, when I talked about 5% failure chance per cycle that's what I meant. And 5% is probably an underestimate.
If you're regularly testing your drive's ability to be heavily loaded for a few hours, you don't have much chance of failure during a rebuild.