They are not, but they are better at swallowing the errors and not bothering you with such details. ZFS fails fast & early, while EXT4 will fail when you realize your Postgres DB is borked.

I guess it's possible that some type of disk command timing could cause unexpected lockups or slowdowns that you wouldn't get with a system that doesn't try to control the hardware to quite the same extent as ZFS, but my (cursory) understanding is that it's rare/hardware specific.

My personal take is that running ZFS on hardware that lies is no worse than running EXT4 on it. YMMV as I'm not a storage expert.

Search online for published papers related to "IRON File Systems." Some researchers injected errors into various parts of common file systems and see how well they recovered. I think ZFS was the best of the bunch though that research is from a few years back and things may have improved elsewhere.

The IRON paper doesn't mention ZFS, I found some citing papers that focus on ZFS but have no comparisons.

Yes you are right. I believe it was a different paper by the same research group... http://pages.cs.wisc.edu/~kadav/zfs/zfsrel.pdf

If the storage lies about syncs, the best you can hope for is replaying a consistent state somewhere in the past. Log structured filesystems with checksums would be a good bet here.

The short answer is no.

Short answer "no" with a longer answer of "ZFS is sometimes better than most other options"