The myth in "To understand C++, you must first learn C" is not that C and C++ are unrelated. The myth is that learning C helps you understand C++. The reality is that telling people to learn C first is an excellent way of getting them to write really bad C++ when they switch over to C++11.
Although true, I feel this argument is rather weak: it's true, that when teaching I wouldn't want to start with pointers and malloc's from the get go, but it does not mean C++ is the only alternative.
If you're teaching systems programming, don't hide pointers. In this case, knowing the addition operator is useful iff they understand the underlying operations.... chances are, if they're learning C++, they don't.
It's difficult to find a place for C++ in my little projects, given that I can use C for low level stuff and Python or Lua for high level stuff.
But got to say, my experiences with learning C++11 has changed how I view C++, it's much more robust and nice environment than what I thought, the new C++11 and C++14 really bring some nice things to the table.
I'm not really sure about the rest of the myths. I'm a little confused about how "To understand C++, you must first learn C” is a myth since C++ is a superset of C so you kind of have to learn C.
[1] http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n227...