> The return type of comparison operators is entirely irrelevant

It is entirely relevant. The boolean type of the language is whatever is the type of (0 < 1).

> Typedefs have their own namespace anyway

Typedefs positively do not have their own namespace.

If you write

  #undef getc
  {
     typedef char getc;

  }

you cannot call the getc function in that scope; it is now the typedef.