However, Application code is calling all these nightmarish library functions which you don’t understand and have to rely heavily on documentation and experimentation to use. It’s not like that at all in e.g. Java, where reading the standard library code is a pleasant and educating practice.

This is good because unlike Java, for C++ there are several standard library implementations so relying on something that happens to be guaranteed by one is not a good idea. The standard and documentation is the only place where you will find what is actually guaranteed to work.

Please stop this FUD. I have zero trouble using std::whatever in C++ without diving into their code. Usage is very well though out and user friendly. Higher level libraries do use templates on a different level and are very readable.