If your app uses a huge amount of code, then yes. But that's really the fault of the app developer. Not the library.
What developers often do is pull in a ton of components from the web components catalog and not realize that every component comes with a cost. It's no different than working with libraries. Know the tradeoffs.
https://ebidel.github.io/polymer-experiments/polymersummit/f... is another example that shows how to utilize the "upgrade" feature [1] of the custom elements API. IOW, the browser can render markup without JS ever running. Unfortunately, this is not something that Polymer leverages very much. It requires more work and is less friendly to new developers.
What developers often do is pull in a ton of components from the web components catalog and not realize that every component comes with a cost. It's no different than working with libraries. Know the tradeoffs.
There are plenty of examples of fast rendering apps that written with Polymer. Check out https://shop.polymer-project.org/ and https://www.chromestatus.com/features, to name two.
https://ebidel.github.io/polymer-experiments/polymersummit/f... is another example that shows how to utilize the "upgrade" feature [1] of the custom elements API. IOW, the browser can render markup without JS ever running. Unfortunately, this is not something that Polymer leverages very much. It requires more work and is less friendly to new developers.
[1]: https://developers.google.com/web/fundamentals/getting-start...