You can select the section you wish from your screen display of a Wikitree descendants page, copy it, then open your word processor or text editor and paste it there. That will give you an editable format, which you can save directly from your word processor. You can also use your word processor to format the content into a table, then save it as a csv file if you wish.
I don't think downloading it to a gedcom file will be of help to you - you would then have to have a family tree program on your computer that could import the gedcom file, after which you still have the problem of getting the format you want out of that program.