These are extremely superficial observations. You should learn more about each of these languages before dismissing them; Go is especially easy to learn.
(I quite dislike Go, actually, but "it has no classes" is nowhere near a valid reason not to learn a language.)
Slow compared to just chucking everything into a single source file, actually: https://github.com/j-jorge/unity-build
That's only true for clean builds and even then isn't universally true, and of course there are other reasons not to do unity builds. But the existence of the technique, and the fact that historically it has sped up build times enough for various projects to adopt it, does show that the C++ model, with headers and separate compilation units, has some inherent inefficiency.