ZFS doesn't have fsck because it already does the equivalent during import, reads and scrubs. Since it's CoW and transaction based, it can rollback to a good state after power loss. So not only does it automatically check and fix things, it's less likely to have a problem from power loss in the first place. I've used it on a home NAS for 10 years, survived many power outages without a UPS. Of course things can go terribly wrong and you end up with an unrecoverable dataset, and a UPS isn't a bad idea for any computer if you want reliability.
Totally agree about mainline kernel inclusion, just makes everything easier and ZFS will always be a weird add-on in Linux.
To me I'd consider Linux not standardized since anything outside the kernel can be swapped out. Want a GUI? There are competing standards, X vs Wayland, with multiple implementations with different feature sets. Want audio? There's ALSA or OSS, then on top of those there is pulse audio, or jack, or pipewire. Multiple desktop environments, which don't just change the look and feel but also how apps need to be written. Heck there are even multiple C/POSIX libraries that can be used.
It certainly can be a strength for flexibility, and distros attempt to create a stable and reliable setup of one set of systems.