I'm familiar with that perspective, and biased towards it... Cloudflare is certainly in such a position, but they are a relatively young company (for their size and reach) and I've seen good things come from them.

I'd guess the intent is unlikely to be anti-competitive or monopolistic, just over-aggressive. However regardless of intent their position does cause an absence of market forces to put pressure on fixing such issues - Similar to how it's become acceptable to have downtime when it's on AWS, because "everyone is affected".

It's true that any wall around you that protects you from something unavoidably comes with a gate that someone else guards, unless you want to guard your gate personally (and that entails filtering out armies of spambots, worst case manually).

As with any power and control you delegate to any entity, only time and good behavior will earn them your trust. That's theoretically what companies are competing for, your loyalty.