Libraries aren't the same as native support as the latter case influences all uses of concurrency in a language while the former only affects things that use that library and may be incompatible with other concurrency libraries.
That seems kinda fallacious. I don't think inherently there is anything that would make an ecosystem around a library weaker than an ecosystem around a language. I.e. if you have a popular actor library then it is not unreasonable to think that there is as rich if not richer ecosystem of things built on top of that library than a niche language with native actors.
