When people say battle tested what they are really doing is looking for bias confirmation. Its no different than when they say software becomes more durable due to community validation.
The only way to be sure is to actually measure things, with numbers, and then compare those numbers to some established baseline. Otherwise its just a guess. The more confident the guess becomes the less probable from the average it becomes. This is how rats out perform humans in weighted accuracy tests in clinical trials.
Not sure what you mean - are you asking number of users, length of time etc?
All I'm saying with this is that ideas which have actually been implemented, used and evolved, are much less likely to have rough edges than something that's never left a whiteboard or spec document. I wasn't expecting that to be controversial.
This stuff is difficult - if I remember correctly the original web components vision was a completely self-contained package of everything - that didn't survive contact with reality - however the things like custom-elements, templating and ES modules are, in my view at least, very useful - and I'd argue they are also the things that had the most precedents - because they were solving real world problems.
People don't need components. They want components because that is the convention familiar to them. This is how JavaScript got classes. Everybody knew it is a really bad idea to put that into the standards and that classes blow out complexity, but the noise was loud enough that they made it in for no utility reason.
The idea that people don't want some sort of improved modularity, encapsulation, reusability, interop etc I think is wrong.
We can argue about whether components as proposed was the right solution, but are you arguing that templates, custom elements and modules have no utility?
Templating, for example, has been implemented in one form or another countless times - the idea that people don't need that seems odd.
Same goes for a js module system, same goes for hiding markup soup behind a custom element.
I could understand an argument from ignorance fallacy wherein your preference is superior to every other alternative because any alternative is unknown to you. But instead, you are saying there is only way one of doing things, components/modularity/templates, and this is the best of that one way's variations, which is just a straw man.
You really aren't limited to doing this work the React way, or any framework way. If you want to continue doing it the React way then just continue to use React, which continues to evolve its own flavor.
And web components are an extremely shitty half-baked near-solution to any of those.
What battle testing? Literally nothing in Web Components was ever battle-tested before release. You wouldn't need 20+ specs to paper over the holes in the design had they actually veen battle-tested.