But why do you need it? Being on top of HN with 10,000 visitors doesn't kill a simple static site. Likewise, a client-rendered web-app shouldn't be too much for a simple server.
It makes sense to use those services for all the additional stuff, like Netlify's offers:
>User identity, Serverless functions, Instant forms, Split testing & rollouts, Analytics, Large media
I think it isn't so much about what traffic to a static site will do to a server, but rather what the experience is for the end user. The tie in to CDNs help reduce load time for your end user.
Yet web-apps are made to not be bothered by load-times. Web-apps are cached by the browser. Once downloaded, startup-time should be instantly.
And downloads shouldn't take too long. Basic 1Gbit connections give you 100Mbyte per second, 10M per 100mils. A landing page should be doable in 10M, and then there is at least one second left to load the rest of the page before the user can react and make a choice.
In the case you mentioned (top of HN with 10,000 visitors), each user would be loading the full webapp for the first time, so I think caching would be mostly irrelevant.
It makes sense to use those services for all the additional stuff, like Netlify's offers:
>User identity, Serverless functions, Instant forms, Split testing & rollouts, Analytics, Large media
But for a basic web-app, where's the benefit?