Fast utility (on Mac) for copying a civ into a specific worksheet in a preexisting excel file? [closed]

I have a set of python-based analytical processes that digest and generate relatively large amounts of data, which I then put into Excel files for use by the rest of the business (in addition to the raw data tabs, the excels have various formatting, pivot tables, etc that I’m not willing to put aside).

In python, I can use pandas.to_excel(...) to write to a specific tab/worksheet in the existing files. But it is SLOW. By contrast pandas.to_csv(...) is very fast. But then I have the data not sitting in the excel.

Is there a relatively fast process (likely outside pandas, potentially outside python) to copy bulk data from a csv to a specific worksheet in an excel file?

(I’m on a Mac if that helps)

Thanks!
/YGA