When deleting a mod from the Arma Launcher it removes a shortcut only (not the actual mod files) in SteamLibrary\steamapps\common\Arma 3\!Workshop
However, it does not remove the actual mod from the workshop itself, only the above shortcut.
It would be great if it did delete the workshop mod located in this folder instead: SteamLibrary\steamapps\workshop\content\107410\mod-id-number-folder-here