I mean, UEFI was broken by design from the get-go. It was entirely designed around Windows and shims were an afterthought once the rest of the industry figured out they’d be fucked if they allowed Microsoft complete control. But they didn’t fight for an overhaul because Microsoft got all its OEM and BIOS makers on board.

So shims are the best next thing, and they aren’t just about Linux, they’re a second PKI layer that allows other entities (than Microsoft) to sign shims. Those entities can be Linux distros but also other OS, software or hardware makers.

Microsoft forgetting to revoke signatures for old shims is orthogonal to the design, but it’s also true that it’s not a very good design. Again, because it was originally made to only deal with Windows and does not deal well with other stuff. The article goes into some detail about workarounds on top of workarounds.