Are these typical build speeds on static sites these days? It's slower than I expected for a rust re-write. (Or I guess maybe the portion re-written in rust is only a small part of the build pipeline time?)

My understanding is that astro isn't considered particularly slow?

Yeah, the parts rewritten in Rust here as only parts of the bottleneck. A lot of it is still JavaScript (including the user's code!). If Astro was just .md -> HTML, it'd of course be much faster.