To get into VRS you need to be travelling downwards at over half the speed of your downwash and an S61 has far more than 600'/min downwash, more like 2000'/min.
It is all about disc loading - older helicopters had low downwash speeds because engine power was lower and the rotor had to be bigger.
Modern helos have very powerful engines and smaller rotors for the same or increased AUM.
Nick Lappos published a RoD vs Fwd speed diagram for VRS produced, I think, by the US Army. The VRS boundary was related to downwash speed - you needed 0.6 to 0.8 of your downwash speed to catch it up enough to start to ingest it.
https://www.rotorandwing.com/2011/11...wash-velocity/