so you seems to have a very special hoster or something else. what you wrote is b........it and totally wrong.
1. If you install the module via WB admin you can uninstall it via WB admin without any problems no matter what group the wwwrun-user has, because it is in both cases (install and uninstall) the same.
2. If you have uploaded the module via ftp and manually created the database the only way to uninstall is to delete the files via ftp and manually delete the database.
The only thing what is not possible and this is discussed her thousands of times is mixing this versions, mean install via ftp ant uninstall via WB admin. If you have no problems you or your hoster changed something on ownerships and/or permissions, but this is no WB problem, this is a problem caused from you (or your hoster).
To get files deleted per ftp wich owns the wwwrun user, simply change the ownership to ftp then you can delete all files. And if you do uninstall a modul manually via ftp please delete also all tables and tableentries from this modul.