What is the advantage of Z-10 vs smaller helicopters like Z-19?
Z-10 is a 7t class medium weight attack helicopter, Z-19 is a 4t class lightweight recon attack helicopter.
The usual benefits of heavier weight means Z-10 can be more heavily armed, more heavily armoured, have more potent sensors and datalinking, and greater range and/or endurance, or a combination of these factors, compared to Z-19.
Heavy attack helicopters (in the 10t weight class) like AH-64, Ka-52, Mi-28 all in turn have those advantages to an even greater extent.
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And before anyone asks, yes there have been rumours for a few years that a 10t class heavyweight attack helicopter based off the Z-20 drivetrain and airframe is in the works, and no there are no recent update or rumours about it that we're aware of.