Think you are overstating its importance, but I do agree the language’s biggest pitfalls are easily right here. That said, if you start from first principles and force every feature and construct to be justified ruthlessly, it’s easier to see how they got there. Constness (as a type concept) and immutability are one of those things that can explode into surprising complexity for the language and compiler.

In retrospect, it may have been worth the pain. Maybe in the distant future, Go will have it. For now, if you want a more sophisticated language, options exist, with all the tradeoffs that will entail.