Depends, mainly because 'academia' is far too broad of a term. For starters not all professors teach the same amount of hours (don't know all rules across all universities but there might very well be professors who do not teach at all but instead have PhD students do it, or post-docs). Professors which have anough funding can hire people for administrative work; though they'd still have to take care of getting funding usually whih is also a huge time sink. In some fields professors actually do practical work themselves, or are very close to it. Not all fields can realy on the same amount of literature-only studies. In some fields with novel research there might not even be literature to use. And so on.