No
Z-20 is a 10 ton utility helicopter, like Blackhawk.
Z-21 is an equivalent weight attack helicopter, which for a 10 ton attack helicopter is a heavy attack helicopter like AH-64.
AH-64 and Blackhawk share the same T700 powerplant.
Z-20 and Z-21 share the same WZ-10 powerplant (not to mention other things like rotor, transmission, structural elements etc).
What makes you think a 10 ton class attack helicopter isn't a heavy attack helicopter?