Partitive is a spoken form, rather than a literary one. So "have to" is a bit strong. I don't know French, so if it the case here, you may say "to try to keep partitive you need to" but you don't have to keep it, as if one form is a literary one in one language and a spoken one in another, the translation suffers anyway.when you would use de/du in a partitive sense in French, you will have to use the Genitive in Russian
Linguistically, they virtually have no isoglosses separating them, plus Prussian lies in many senses between Slavic and East Baltic. Simply, Lithuanian in many aspects has preserved the habit Slavic languages had some 2-2,5 thousand years ago — it is like comparing early Runic Norse and modern English.I think the categorization into Balto-Slavic languages may be partially at fault.