As someone who has tried to find a way to help content authors develop and maintain big web sites by creating (HTML) components for years, I\'m really excited to see web compone
I've had similar misgivings about web-components myself, but then I started working with third-party React components. They have the same problems in that they bring along all their own dependencies. But worse than that, because React doesn't like living with other versions of React, React components must list React as a Peer Dependency. This means that you are forced to use the same version of React as your third-party components.
So my conclusion is that this is in fact a feature of web-components! Every Custom Element can have it's own dependencies entirely independent from the rest of your app. I consider third-party components to be the main use-case for Web Components; where the consumer wants to be able to use a component with as little friction as possible. Sure there will be some duplicate code, but the component consumer doesn't need to know or care. I think that component authors will deal with this is by using smaller modules in their components. For example, instead of using React they could use something like Snabbdom.
If you are building an entire application out of web-components that you control, you can still use a bundling tool like Browserify or WebPack to manage your dependencies. These will allow you to override certain modules so that you can even force third-party components to use the same versions as the rest of your app (see: https://www.npmjs.com/package/aliasify). That might break some modules, but that's life.