I'm a bit sceptical about the comparison of optimisation. Specifically when the AST was mentioned (did they parse the expression as Python code?) and Python came out that much slower even after fixes. As long as they were interpreting that, rather than compiling the expression into native code, I don't see a good reason for Go to be faster. Interpreting expressions like that in Go would be almost as dynamic / lookup heavy as in Python.
I'd like to see both apps for comparison / more context.
Although, if I spent over 2 weeks developing and optimizing a solution in Language A, I would fully expect to develop and optimize it an awful lot quicker in Language B.
Additionally, a lot of performance issues can depend very much on what libraries are used.
That basically confirms the strength and weakness of python : it's very good for prototyping and if performance issues arise (and that can be later than one think), it's tough to optimize.