Maybe add a CDN. This shit isn't rocket science and being able to accurately monitor your own systems from off infrastructure is the one time you should really be separate.
They could have a related outage, or even a coincidentally timed one
Why not? The big tech companies use each other all the time.
For example, set up a new firewall on macOS and you can see how many times Apple pulls data from Amazon or Azure or other competitors' APIs and services.
The postulation was that Apple and Amazon weren't competitors. Not that they're not competitors in a specific niche.
Apple uses their competitor's services because they can't build their own cloud and host their own shit. The big boys don't use competitors for services they are capable of building themselves.