As someone who tried TrueNAS at first, but prefers declarative reproducible configuration, do give NixOS a try. Best NAS base-OS I've tried so far, and when it was time to migrate to new hardware, I just switched the disks, re-ran the config and was up and running in no-time.
Ok, sounds complicated compared to a basic FreeBSD install.
I dont think its much more or less complicated, just depends on which one you're more familiar with.