Google has a C++ race detector based on the Go one and it did not detect this issue (or was ignored).
Neither of those things you listed reduce the severity of the bug, and both are available in well written C++ code as google tends to do.
Go compiles down to machine code, it has a stack and heap, it has structures on that stack and heap, and it has data races; those are all of the required components for a use after free. You can have data races compiled by the stock go compiler without the use of unsafe (also, why have race detector tooling if this is false?). It would probably be easier to exploit than here even because one wouldn't even need to bother with the ASLR pointer exfiltration they had to do here.
It may be harder to write exploitable code, but memory safety does not guarantee runtime memory safety. Especially in the face of concurrency.
Source (scroll down to the conclusion section): https://blog.stalkr.net/2015/04/golang-data-races-to-break-m...
Go has a garbage collector (i.e memory safety) & race detection tooling built in. https://golang.org/doc/articles/race_detector.html
Even if a race condition bug does sneak in, it won't be as catastrophic as C/C++.
Writing concurrent code is hard in any language. There's no magic bullet & Go or Rust are not immune to concurrency bugs. If anything, tools like the race detector should always come built in and every dev working on concurrent code should use one.