Cloudflare is really good at what they do, they employ good engineering talent, and they understand the problem. That lowers the chance of anything bad happening. On the other hand, they achieve that by unifying the infrastructure for a large part of the internet, raising the impact.
The website operator herself might be worse at implementing and maintaining the system, which would raise the chance of an outage. Conversely, it would also only affect her website, lowering the impact.
I don't think there's anything to dispute in that description. The discussion then is if cloudflares good engineering lowers the chance of an outage happening more than it raises the impact. In other words, the things we can disagree about is the scaling factors, the core of the argument seems reasonable to me.