Does anyone know what they could mean here? I get that having more open connections and slow requests is not great, but there are popular attacks people will try against them in this case. They already have to handle pathologic cases of slow requests, so handling some small number of slower clients shouldn't be an issue.
Or are they talking about some other problem?
Just try one of the akamai endpoints to test it. (E.g media.steampowered.com)
For me 1.1.1.1 serves akamai singapore IPs, while 8.8.8.8 serves IPs of my ISPs akamai cache in Sri Lanka.
If your ISP has a bad route to 1.1.1.1, this just gets worse.
In what case would some extra delay be worse than no access at all?
We really dont know the site works in the backend. So I guess the admin did not want to spend time to fix issues cloudflare created.
But that's the thing, Cloudflare didn't really create any issues. If I live in the US and I decide to use some random public DNS server in Australia, it will be an unpleasant setup, but it's a perfectly valid one.
There's no rule that your DNS server must be on the same network as you, or send your subenet if it isn't. When that's the case it allows for some nice performance optimizations. (I.E. sending you to a closer cache.) But it's just that - an optimization. If your service is completely unreachable without performance optimizations, you've created a very fragile service.
It's the default configuration. 99% of internet users follow this configuration (at least, until web browsers start shipping DoH as a default). It's honestly a fairly reasonable assumption to make.