Comment by kyledrake
There are also alternatives to Cloudflare and AWS, that didn't stop their outages from taking down pretty much the entire internet. I'm not sure what your point is, pretty much everybody is using let's encrypt and it will very much be a huge outage event for the web if something were to go seriously wrong with it.
One key difference: A cert is a “pickled” thing, it’s stored and kept until it is successfully renewed. So if you attempt to renew at day 30 and LE is down, then you still have nearly more than two weeks to retrieve a new cert. Hopefully LE will get on their feet again within that time. Otherwise you have Google, ZeroSSL, etc where you can fetch a replacement cert.