The problem is, the community collectively decided the problem was "threading" in general rather than "trying to have tons of threads running around shared data structures controlled via piles of simultaneously-held semaphores" specifically.

If you don't structure your threads on that basis, but instead default to something that looks more like actors and message passing, even if it isn't strictly speaking actors and message passing, the complexity comes down. Add some later elaborations like structured concurrency and a few other pre-canned design patterns for threading like a parallel map or worker pools being issued work items and it becomes merely something difficult rather than insane. When you program with threads sanely, it takes very little for async/await to actually be the substantially more complicated and difficult-to-understand choice when you have a workflow more interesting than "always await everything immediately" to implement, to say nothing of how nice it is to have things actually running on multiple cores simultaneously without having to carefully arrange for it.