The javax.xml.stream package has been included to allow for streamed reading of the excel sheet, if I recall correctly specifically for the XLSX files.
The additional libraries that are included with the excel importer module where necessary because of some class loading issues in the past that prevented usage of the javax.xml classes supplied with Java.
This package has not been modified and it's still the standard library.
We want to include as few libraries as we can, so we should definitely test if all cases of the excel importer can be handled without this library.
In older 5.x version I know it had a function, but this might no longer be relevant. We can test this and might be able to change or remove this library.
This library kills my own xml export/import stuff. I removed it and the excel import works just fine. I think it was included for the template export/import functions