I have some experience managing servers that were targeted by script kiddies using services like this. Dealing with the attacks is usually pretty simple due to clear ways to identify the traffic (i.e. the bots all have the same useragent). However, if they're powerful enough to fully saturate your connection, you're going to have a tougher time. It's great that sysadmins can mostly get away with just paying for CloudFlare, nowadays.

What actually surprises me more about this article is that he is operating in the United States. However, I'm not sure the value of an "FBI backdoor" in this situation. People "renting a botnet" are not usually important people that I'd think the FBI should be spending their budget on.