Maybe bulletproof is a bit strong but I mean, it was fine on DOS/Windows for decades. I never lost data due to filesystem corruption on those computers. Media failures, yes frequently in the days of floppy disks.
I had a HD fail on me while using Windows 98 as main OS, yet thanks to ext, I think it was ext2 at the time this happened, I still managed to repurpose it for Linux, for several months.
It was ok from possible data failures point of view, I didn't had much data other than the distro and the stuff I also needed to compile under Linux.
Somehow it managed to still work with the disk, with the sectors that were not damaged.
The bulk of the safety came from the redundancy of copying the file across machines, not filesystem protections.