The guy I replied to is saying that he needs to use third party libraries just for state management and data binding. Pretty much every non-trivial component is going to need these features, and if they're using a library to get them, we're back to the same situation we were in before Web Components.

Nope.

The whole point of Web Components is that all of the innards of components are completely encapsulated in a component, the 'client' of a component only cares about setting its attributes and responding to the events that it emits. (And perhaps supplying external styles.)

I also think your claim of having to use 3rd party libraries for anything non-trivial is false, but let's ignore that for now.