We’ve seen what the Russian military has been like in Ukraine, if you think most of those subs aren’t rusting piles of garbage then you’re probably drinking that tankie Kool aid. They’ve probably had to cannibalize the majority of them just to keep what few they have running, because it’s not like they just idly make parts for 1950’s era subs, especially not for a country that barely has enough money to feed themselves and spends most of that on their nuclear program.
Also they’re loud ass diesel subs, every modern navy will know exactly where they are and how many they have easily, and it’s not like 1950’s weaponry is going to make up the difference.