A pointless abstraction layer? Let me remind you that DMS is the archiver we used to spread disks with in the old days, not a tool that was invented in the interim to make emulation more cumbersome.
For me personally, I find using DMS on the Amiga to create disks far more convenient than the additional steps I have to take to convert an adf to an actual disk. I know many will disagree with this, but that's my experience (outside of FMS devices, that is).
And neither DMS nor PowerPacker have given me any more instances of errors inherently. The only PowerPacker files I have had any issues with have been from mutant versions which have been hacked to try to prevent decompression. Maybe they wanted the same level of unreliability as address crunchers? The DMS files that you see corrupted are that way due to being written to disks with sector errors. I have seen this same problem with every other file format, since any file is prone to corruption if written to a bad disk.
The real 'usable format' you speak of is for emulators. But there's still a community out there who prefer using the real thing and I like to think they get a higher priority.