Even Latin, with only five (or six if you count the vestigial vocative) cases needs prepositions to carry some of the load.

I've never heard of a language without pre- or postpositions. Do you know of one? Even Finnish with 14 or 15 cases has postpositions. Hindi only has two cases and two numbers, the direct and the oblique, a far cry from Sanskrit's 8 cases and 3 numbers (it has a dual number besides singular and plural).