Superset II is definitely chrome molybdenum steel, made by Tange in Japan to Bianchi's custom specifications. My understanding is that the main tweaks Bianchi made were to the top tube (slightly smaller) and the down tube (slightly oversized/ovalized at the BB juncture).

What that means is it's a substantial bit lighter than Tange's MTB, and close in weight to Tange/Logic tubing (which was pretty lightweight for non-heat treated CrMo). It's decent stuff, meant for lugged-frame construction.

I have a Bianchi Boardwalk hybrid set up for gravel/cross, and that one is also made with Superset II. The ride is compliant, without being squishy. It's definitely much less harsh than the MTB tubeset ever was, and slightly less sharp than the Prestige line was.