> It's not a ridiculous question to ask "will my compile times be longer if
> I port project X to C++." The answer is almost certainly yes.
That's simply not credible. If it was a port from C, there is nothing a C++ compiler would do differently than a C compiler that would greatly increase compile time.
> Every large C++ project I've ever worked on has had long compilation
That's a valid observation but it doesn't indicate any general statements can be made.
> It's a consequence of the design of the language.
That does not follow.
> Every file in a C++ project must do the same work over and over for
> #include directives. A single #define could change the meaning of
No, that would be a violation of the ODR. Structures and definitions cannot change after they've been used.
> There is no room for C++ in this world because C++ itself is a layering
Your entire argument makes no sense. There is nothing in C or C++ that prevents or encourages any particular design. One can write well defined modules and interfaces in both languages. One can write poorly structured code in both languages.
But C++ provides safety mechanisms that are simply not available in C. RAII is an example.