I'm with you on 'declarative' but I'm always sceptical about 'semantic'. Its meaning is vague, its benefits somewhat ethereal and its actual existence in the real world a matter of rumour and speculation.
If you can pin down your definition then I'd be able to provide a more concrete opinion.
> The notion of separation between information, presentation and behavior couldn't be any more fundamental.
Fundamental to whom? Outside of web development this separation was never fundamental - see the post above regarding "separation of concerns" - which is a much better candidate for a "fundamental principle"
In the long run, the SPA craze will backfire, big time. Rect components are not semantic and not declarative. There is no way to examine them without executing code. This is an elephant in the room most fronted developers willfully ignore right now.