It's pretty easy to make a carbon steel blade hard, just quench it and don't temper it. In general, very hard blades are not practical as while they will hold an edge for a long time the difficulty in putting that edge back once it's blunt can be a problem for many people. One reason butcher's liked Victorinox butcher knives, plain carbon steel that was easy for them to keep sharp. Same with chefs.
It would be an interesting experiment to try tempering one of those W Rose knives, or re-heat, quench and temper to see what effect it has. Not going to happen, of course, as anyone who has one is unlikely to want to try it.