You can build user defined functions in Excel with VBA as well as with Python through something like xlwings. One of the issues that I ran into with xlwings (or any third party integration into the Office suite) is portability between users.
The ubiquity of Excel is both a blessing and a curse in that everyone has it, so everyone uses it, regardless of whether or not it is the best tool for the job.
The ubiquity of Excel is both a blessing and a curse in that everyone has it, so everyone uses it, regardless of whether or not it is the best tool for the job.