Thought process is: Peertube or some other service’s first job is the purpose for the service, so security likely won’t be as good as a service who’s first job is security.

Really good point. I see many selfhost instructions now that say 'we don't bother with HTTPS, just use a proxy to handle that' and maybe auth should go the same way as in there's good solutions that specialise in auth so it's not worth each project doing it themselves.

apps can’t deal with hitting Authentik 1st afaik

Another good consideration. There is an early Peertube app but I doubt my users will be using it, web access is fine for this. Perhaps apps for things like Lemmy/Mastodon/Peertube etc will need to work better with these auth frontends in future.