For example, I have hear many times, about large investments (millions) into C++ web frameworks, or even made some really large backends in C++ (evernote). And they mostly have not much success, because exists much more suited platforms for web.
You sure could argue that Go is fast, and i will absolutely agree - Go is very good in its main niches, but in real life web dev, speed of language usually is not MOST limiting factor - mostly limiting db, file access, system calls.
Imagine, how large should be project (or how special), to include db, fs, sc inside Go, to avoid those slow things so much, so speed of lang itself will matter.
BTW, for slow dynamic languages, people have success running Python Django on Cython, which is compiled to native code via C, and it is very fast, and basically, Cython is just compiled Python, most code work without significant changes.
So sorry for many words. To be constructive, if I will be in place, where have to find Golang web framework, I will try to find viable C++ web framework, and make bindings, so in beginning will replace some modules with Go modules, and in long time perspective, rewrite all C++ code to Go. All other solutions, I could imagine, are too stranger for Go.
Most important difference, is that Ruby itself could been used as script language for declarations; Python is less suited for declarations, but also possible; most usable functional languages (Python is semi-functional), or languages with very powerful preprocessor (like most functional are); json is just subset of javascript.
But for C-like languages (Java, C#, Objective-C, etc), need to make compiler or interpreter of Domain Specific Language (lua, or some intermediates), which will be used to define system structure, or use some sort of XML/json/yml or binary editor, to define structure (as in Android and in Ios).
For example, Java Spring use boot assembler, specially created to parse declarative configurations of framework, and to apply some logic.