To be clear I don't believe that, but that's analogous to what I hear when I see this.
LiveView has composition of components, so there's an immediate answer to your question. You've already answered another piece with built-in soft real-time.
In all honesty, if you have looked at LiveView and don't understand what it brings then I'm not sure if you looked sincerely.
React and similar technologies actually not just scrap your boilerplates, it's real abstraction (forget the DOM API) with state and componentation. It's not like you scrap your jquery boilerplate).
I see people mess with DOM Api in their application, which is not the right way, because it's mixing different abstractions together to create a mess.
It's a complete way to build complex apps. I've personally built fairly decent complexity SaaS (18mo of dev) completely on LiveView + some react when it made sense.
Saying it's just HTML pushed over WebSocket is like saying React is just virtual DOM with components. There's much more to it when you get into it.
Plus it's enjoyable. I had significantly more fun and development speed building on it than the typical React+API approach.
That said it's still situational and I don't blindly recommend it to everyone. I think Elixir has one of the best graphql implementations (Absinthe), so I still recommend React+GQL as well.
I found people who's stuck in DOM abstraction like React keeps reinvesting what platform is already capable of. Some abstract is so nasty e.g. forwardRef .. like really? Real Event bubbling is so much better, it visit every damn node you got the ref for free.