While what you say is true, it is irrelevant in the context of the discussion here about the popular misunderstanding of pierogi ruskie. This confusion is due to multiple factors than just “Russia stole”, including that the Ukrainian-language literary canon is centered around “Ukrainian” as the ethnonym, instead of making any attempt to preserve or revive the ethnonym “Rus”. While some Rusyns did maintain the ethnonym, other Rusyn speakers have preferred to identify with another ethnonym instead. If East Slavs other than Russians and Belarussians did not stand up for the ethnonym en masse, no surprise that peoples elsewhere no longer have the ability to distinguish.