If you're handling billions of requests per second, you're not a self hoster. That's a commercial service with a dedicated team to handle traffic around the clock. Most ISPs probably don't even operate lines that big
To put that in perspective, even if they're sending empty TCP packets, "several billion" pps is 200 to 1800 gigabits of traffic, depending on what you mean by that. Add a cookieless HTTP payload and you're at many terabits per second. The average self hoster is more likely to get struck by lightning than encounter and need protection from this (even without considering the, probably modest, consequences of being offline a few hours if it does happen)
Edit: off by a factor of 60, whoops. Thanks to u/Gud for pointing that out. I stand by the conclusion though: less likely to occur than getting struck by lightning (or maybe it's around equally likely now? But somewhere in that ballpark) and the consequences of being down for a few hours are generally not catastrophic anyway. You can always still put big brother in front if this event does happen to you and your ISP can't quickly drop the abusive traffic