The original "tale", of which it isn't, was from the Bell 214B for the reasons here and the resultant "ballistic" trajectory.
6000 FPM at SL wasn't/isn't difficult light but you could also cave in the greenhouse windows above your head. Not rated for 60 knots vertical and above. Even an old 205 will surprise some when light and you can bust the windows in one as well.
Apparently a 214 back in the day established a couple of records and sustained ~2000 FPM to 30,000' and ~5200 FPM to 10,000'. So the rate numbers at sea level would have been higher.