> Typedefs and variable namens don't live in them same namespace, do they?

Depends. See this snippet: https://www.godbolt.org/z/5T5jz47q4

Cannot declare a variable called `u8` when there is a typedef of `u8`.

And even when you can declare a variable called (for example) `int`, that effectively "breaks" the program by not being even a tiny bit readable anymore.