Shadow DOM and custom tags make it possible to closely mimic the way we used to do UI development back in the Delphi/VB6 era. I like how eg. css properties only apply to a given component.
Polymer seemed like the most lightweight possible way to implement this because it uses the browser facilities. I understand that React also has components and custom tags (JSX) but it doesn't use browser facilities but rather implements them itself, which just sounds like the wrong way of approaching the problem.
It is true that polymer had quite a bit of limitations, but there are other solutions like stencil, lit-element, svelte or vue (yes it can output WC's) that do not have those problems.
Lit-html in latest version I think is only outperformed by inferno from popular solutions.
This is not true, there is no string conversion. There is even separate syntax for setting props vs attrs.
Check out the readme here.
https://github.com/Polymer/lit-element
I also normally use redux in my WC applications.
Still my favorite one is "Commas in literal strings: Any comma occurring in a string literal must be escaped using a backslash (\)." here: https://polymer-library.polymer-project.org/3.0/docs/devguid...
React is Javascript through and through, and yes, it only uses browser facilities. Because JSX is not custom tags, it's function calls: https://reactjs.org/docs/react-without-jsx.html