Hi Heikke,
you are right, there is no views/favs ratio option. However you still can renew listings with highest/lowest number of views/favorites (not their ratio).
Please check
https://seller-tools.com/seo/etsy/renewals/manager/schedules/add/ and for "Renewals order" field select any of:
- Items with highest views number
- Items with lowest views number
- Items with highest admirers number
- Items with lowest admirers number
We'll consider adding the ratio sorting option based on your request.
I hope this helps.