First, let’s set aside the separate question of whether monopolies are bad. They are not good but that’s not the issue here.
As to architecture:
Cloudflare has had some outages recently. However, what’s their uptime over the longer term? If an individual site took on the infra challenges themselves, would they achieve better? I don’t think so.
But there’s a more interesting argument in favour of the status quo.
Assuming cloudflare’s uptime is above average, outages affecting everything at once is actually better for the average internet user.
It might not be intuitive but think about it.
How many Internet services does someone depend on to accomplish something such as their work over a given hour? Maybe 10 directly, and another 100 indirectly? (Make up your own answer, but it’s probably quite a few).
If everything goes offline for one hour per year at the same time, then a person is blocked and unproductive for an hour per year.
On the other hand, if each service experiences the same hour per year of downtime but at different times, then the person is likely to be blocked for closer to 100 hours per year.
It’s not really bad end user experience that every service uses cloudflare. It’s more-so a question of why is cloudflare’s stability seeming to go downhill?
And that’s a fair question. Because if their reliability is below average, then the value prop evaporates.
Why is that the only option? Cloudflare could offer solutions that let people run their software themselves, after paying some license fee. Or there could be many companies people use instead, instead of everyone flocking to one because of cargoculting "You need a CDN like Cloudflare before you launch your startup bro".
Cloudflare isn’t the only game in town either. Akamai, Google, AWS, etc all have good solutions. I’ve used all of these at jobs I’ve worked at and the only poor choice has been to not use one at all.