The collectors need enough smarts to detect that an IP address is behaving legitimately, and when the behavior changes sufficiently that it's no long legitimate, to stop accepting data from that traffic.
If you're talking source IP spoofing - that's only UDP, we don't offer anything other than DNS over UDP, and that's now being served by Cloudflare, so we can just ignore all UDP packets. Sure people can spoof SYN, but that's not a very powerful complexity attack.
