Hard to sharpen just means different things to different people... honestly the amount of steel in such a thin profile should be a breeze to remove regardless the steel. Can the steel support a 15 deg edge is a whole other question... large carbide steels may not. Steels with high % retained austinite will struggle. But it is not hard to remove enough steel. Just make it have a proper edge. My question is actually what are we dealing with. O1 that is very hard is easier to sharpen to a fine edge than O1 that is too soft.