The Rus peoples arose in the 9th centuries when the East Slavic tribes invited the Rurikids to rule over them and formed the Rus.
Prior to that, it was Khazar and prior to that, Iranic speaking Sarmatian and prior to that Iranic speaking Scythian territories. Not to mention parts that were East Germanic tribes, Greek city states, etc. etc.
And after the Rus coalesced, then most of the coastal areas were not Slavic but various TurkiC tribes
Not even in 1400 AD do we see "part of the Rus people's territory"
Your "always" seems to date from 1750 onwards