“you can read the source code of 100% of these functions (unlike with Mathematica)” This is an important observation. The source is the ultimate documentation,

“you can read the source code of 100% of these functions (unlike with Mathematica)” This is an important observation. The source is the ultimate documentation, and, in many cases (in my experience) the only correct documentation for a software system. If you can’t see the source, you don’t know what the program does, you only know what someone says it does (aside from exhaustive experimentation).