>So why is it fundamentally and obviously true for PQC? This isn't actually an engineering hill I'd die on, if more people I trust made clear arguments for why this is dangerous I'd take it very seriously, but right now we basically have djb against the entire world writing a blogpost that makes ludicrous insinuations and fails to actually engage with any of the counterarguments, and look just no.
As a response to this only, while djb's recent blog posts have adopted a slightly crackpotish writing style, PQC hybridization is not a fringe idea, and is not deployed because of djb's rants.
Over in Europe, German BSI and French ANSSI both strongly recommend hybrid schemes. As noted in the blog, previous Google and Cloudflare experiments have deployed hybrids. This was at an earlier stage in the process, but the long history of lattices that is sometimes being used as a (reasonable) argument against hybrids applied equally when those experiments were deployed, so here I'm arguing that the choice made at the time is still reasonably today, since the history hasn't changed.
Yes, there is also a more general "lots of PQC fell quite dramatically" sentiment at play that doesn't attempt to separate SIKE and MLKEM. That part I'm happy to see criticized, but I think the broader point stands. Hybrids are a reasonable position, actually. It's fine.