It's interesting because there have been so many web developers over the years who been given the advice that a variety of 3rd party CDNs was "faster" and did t

It's interesting because there have been so many web developers over the years who been given the advice that a variety of 3rd party CDNs was "faster" and did that intentionally. It may have even been somewhat decent advice for a time. Mostly because of the 6 requests per host blocking in browsers: more hosts, more parallel requests. Of course parallelizing requests isn't always faster, especially as you point out if some of those CDNs underserve certain edges. Plus, HTTP/2 and HTTP/3 change some of the dynamics of that directly (by massively decreasing connection overhead to the same host so that even "blocked/serial" requests may finish a lot faster than the time it takes to open a full connection to a different host). Sometimes for the "if everyone uses the same CDN for jQuery the browser only has to cache it once for everyone" cache effect, and that is no longer true either as to avoid some privacy issues and such browsers have only further sandboxed their per-website/host caches and even "shared CDNs" no longer guarantee shared caches. But yeah, post-HTTP/2 and privacy-related CDN sandboxing, especially, it is further and further from good advice.