Just timed it, 3k stone with my star metal pick in 3:55 seconds along the beach where stone was plentiful. Either way its not 3 minutes for 10k stone.
Bottom line is Hardened stone needs to be a easier to make, and black ice harder to make, to bring them up to similar time and resource requirement. Yes it is possible to build hardened stone, but requires adjusting many things to be able to build it, building black ice does not require any special adjustments or re specs. If the two were equal you would see a 50/50 split of people using black ice vs hardened stone, or maybe even leaning towards harden stone because of dlc styles. The way it is now it is about 90/10 split for Black ice over hardened stone