There are apps using browser as execution environment and there are websites. You wouldn't expect a client-side drawing tool, WebVR game or real time visualization of blockchain transactions to work without JS enabled.
However, you can easily expect a social network, mail client, news page, task app, and to some extent even things like IM to work with no JavaScript. "That's core" is just an excuse for poor architecture - it's only core because you chose to make it so.
There are apps and there are websites, with only some small part of grey area in between. If you're a web developer wanting to use newest, greatest trendy tools, you see everything as apps, despite of common sense suggesting otherwise, and you end up with no progressive enhancement for no good reason. When you take it to extremes, you end up creating such abominations like the old SPA Twitter frontend, spinning the fans of your laptop for 15 seconds just to display 140 characters of text, because "the core" is implemented as AJAX calls and fully rendered client-side.