Congratulations, now your „password” (the 512-byte random key file) is stored as plaintext on your machine :)
With rate-limiting, non-trivial passwords are not viable to be brute-forced, so making them larger just doesn’t give you much.
I’m running ZFS mirror on Ubuntu on a USFF machine with 2 external USB 2.5’’ drives. I do weekly scrubs, never lost any data even during power loss. Some of the 2.5’’ USB drivers are crap, I had to replace drive 2 times over last 5 years - while one of the drives is with me since the beginning.
I would say that a lot of people over-secure their local home file storage. If you use filesystem (or software) that does checksumming, your home data will be safe. Yeah, in case of power loss you may lose like 2s of last writes on ext4, and that won’t matter much for majority of people because it’s not like it’s your company’s only copy of internal data.
There probably is a clever way that you could do it, but clever ways are easy to overstep, misconfigure and can be unreliable long-term.