APFS not having block or file-level checksums really seems like a big oversight to me. While the filesystem’s designers considered the hardware-level guarantees to be sufficient [1], this issue shows that there is an entire class of problems that they have not considered. Disk images and loopback-mounted filesystems or even disk-level cloning introduce additional layers of complexity where a filesystem can be silently corrupted, even when the actual physical storage layer is perfectly reliable.
A filesystem should be able to last for decades (HFS was designed thirty years ago); I regard not having checksums in a brand new filesystem an over-optimistic tradeoff.