I've learnt my lesson to depend as little as possible on vendors with specific technologies when you want to keep something alive for a long, long time. The less reliance on specific closed-source & cloud technologies, the better.
In this case S3 is just a thing that can serve a static HTML page, which I'm not sure I would consider proprietary in any way, and Cloudflare is just a way to serve it basically for free.
This isn't anything that has proprietary risk of not being supportable/migratable if necessary.
