Using polymer as a JS frontend framework wasted about a year of work at my friend's company. They eventually switched to react for one project and an in-house react replacement for the other.
I'd argue that google is pretty strong when it comes to frameworks, and that most of their criticism comes from people who aren't looking for a framework, but rather a library (like React).
And Polymer isn't even really either of those things, it's a polyfill for a native browser feature.
Polymer is not a polyfill for web components - it is higher level library - something like "jquery for web components" - WC polyfill is separate project, in separate repo - you will need it with X-Tags, Svelte, SkateJS too.