Considering switching to another library because of performance on large files

There are some limitations to box/sprout that would remove some functionality from the module that some people might be using, including "no automatic column widths, no column number/string formatting)" as per the first link you provided.
We could provide the option to choose one of the engines, with the tradeoffs of each library.

Not sure box/spout is still maintained, project is archived on github

Maybe fastexcelwriter ?
https://packagist.org/packages/avadim/fast-excel-writer

Better link: https://github.com/aVadim483/fast-excel-writer

there is any update?