Cloudflare's paid DDoS protection product being able to soak up insane L3/4 DDoS attacks doesn't answer the question as to whether or not the specific product, R2 from Cloudflare which has free egress is able to saturate a pipe.

Cloudflare has the network to do that, but they charge money to do so with their other offerings, so why would they give that to you for free? R2 is not a CDN.