Am I missing something?

The OP's comment is that while Python's native interpreter is slow, Python code as a whole can still be fast since people will delegate the hot spots to non-Python libraries optimized for speed.

To refute that, you linked to John Carmack quoting Horace He saying that Python's native interpreter does CPU-based math slower than a GPU. But...that's why people writing Python use libraries to delegate math-intensive work to a GPU, which is the OP's point.