My (novice) understanding is that embargoes are intended to provide time to 1) develop a patch and 2) distribute the patch.

For Linux/public open source, what you said is right about 2). Once the patch is visible to anyone, it's trivial to identify exploits for unpatched systems. But 1) is still a valid use-case for embargoes for Linux vulns, right? Like, if this patch had taken a few weeks to develop before being confirmed working and published, that's potentially valid grounds for not sharing details during that time (within reason), no?

Linux does actually have a proper embargo process. But, you're correct that in this case it wouldn't usually have been followed anyway. Bugs like this are fixed multiple times a week, anyone with basic kernel knowledge can see that they are potentially LPEs.

Usually, nobody even bothers to check. LPEs like this are too common to even categorise effectively.

The linked announcement specifically mentions that an embargo has been broken.