Quick filters remove rows from the table entirely. RANK() works on the current rows in the table. So you need to filter in a way that doesn't remove rows.
TABLE CALCS used as a filter will not remove the rows. It just removes what is displayed.
Create this calc, put it on your filter shelf in place of your [Vendor] filter. Show Filter. You'll see that it works just like the [Vendor] filter, but it doesn't change your RANK calc.