Nothing you're saying is wrong, but your perspective is totally off.
For someone experienced with C++, or say, Rust (ahem), obviously Go is a bit backwards when it comes to concurrency and race conditions. Obviously you can mimic go's goroutine stacks, obviously you can obtain fast thread switching.
But Go isn't targeting C++ or Rust, and it's not targeting the domains those languages are best at (although admittedly there are some overlaps between Go and Rust). Go is trying to replace Ruby, Python, and JS. For programmers who only know those languages, or haven't had the opportunity to work in more "heavy" languages, Go makes it dead simple and intuitive to do things that previously would have been completely out of reach. All you're arguing is that if you go farther "down" the stack so to speak you can accomplish everything Go does, which of course is true, since it's turtles all the way down.
The fact of the matter is, if someone boots up a brand new linux laptop goroutine switching _will_ be faster than thread switching. That doesn't mean Go is super crazy performant, or better than C++ or Rust, it means someone who's only programming experience is Rails apps can now write performant multi threaded code with orders of magnitude less domain experience. Same with race detectors. Multithreaded Python is a complete minefield for race conditions. Sure, you might not segfault, but you have to think if you use fork() or spawn() depending on the OS, you have to install libraries to detect races, you have to write special tests. With Go all of that comes out of the box and it makes it _easy_.
Go does nothing new, and a lot of languages do things a lot better. Erlang is mentioned in other comments, Erlang is a fantastic language for concurrency and a fantastic language in general. It's also incredibly hard to find programmers who code in it, or are willing to learn it. It's also incredibly hard to sell to the business people higher up. It's also very hard to find Ops people who can competently support an Erlang stack. C++ gives you the power to build formally correct real time systems, but it also gives you the power to blow your whole leg off if you don't know _exactly_ what you're doing. I can go even further down the stack with C and assembly but I think you get the point, it's all about tradeoffs. Go allows programmers to reason and think about concurrency without having to worry about linux kernel PRs, without having to worry about how to share memory, without having to worry about stack performance.
*edited for clarity