That is my point. The Z-18 and H-6K are fine platforms despite their elderly lineage because they are continuations of existing development and experience, i.e. it is resource efficient.
The Z-20 is a brand-new platform and the best China can come up with is a configuration from the 1970s. The Black Hawk platform is over 3.5m longer than NH90 (especially relevant to landing in LZs and operating from ships) and yet lacks the ramp access offered by that platform. It's an old design that has been superseded.
Nope, according to spec sheets from NHI and Sikorsky, overall length of the Blackhawk is not 3.5m longer than the NH90, they are about the same with S-70 being 20cm longer. In terms of fuselage length (assuming folded blades), the NH90 is actually 90cm longer than the Blackhawk. The fuselage width of the NH90 is also 67cm wider than the Blackhawk, yet the Blackhawk is 30cm wider than the NH90 inside the cabin. NH90's cabin is 1m longer, but given that it has a 0.9m longer fuselage, that's not exactly a significant advantage in space use efficiency.
The NH90 has bigger cabin volume mainly because it is taller, but as I said earlier that means more structural weight and a larger side projection making it a bit more susceptible to crosswind. Cabin height is not that critical when not holding tall cargo pallets or ATV, so if those are not a requirement then having a lower profile is advantageous.
We don't know the inside and outside dimensions of the Z-20, nor the radius and center position of the main rotor etc., but with a shorter nose (more compact avionics) and refined aft cabin structure, there is no reason to believe that the Z-20's configuration must be worse than the NH-90 in terms of space use. Not to mention that raw carbin space is not the only factor, it's also about ease of access, adaptability to intended missions, total weight savings, how well are critical components being fitted and protected, etc. Blackhawk's general configuration has been tested extensively in hostile environments, but for the NH90 this is a big unknown.
As I've said earlier, having a tail ramp is not everything, it is not automatically better than having two larger side doors in all situations. The NH90's cargo versatility comes at a cost. This is not a comparison between two general layouts where one is superior to the other on every aspect, this is a comparison between two layouts that balance their capability attributes differently. The reasons you used to suggest otherwise are either inaccurate (about the length) or very limited (that a tricycle gear setup is better for frigate/destroyer based operation). In fact you can shorten the wheelbase like what Sikorsky did to Seahawk but you can't lengthen NH90's wheelbase to increase stability for land use. So I'm not convinced that the NH90 must be an overall better design to follow.
Except that all these airliners look basically the same anyway. A better analogy would be if Y-20 as a clean-sheet aircraft happened to resemble Il-76. We would rightly say that it is out of step with modern design trends, as is Z-20.
They look basically the same because they're being used for pretty much the same purpose. That shows you how half a century old layouts can still be a model for brand new platforms as long as you have similar requirements. The Y-20 looks more like C-17 than Il-76 precisely because the PLAAF wants it to serve roles closer to the C-17 than the Il-76. The C-17 was designed to be able carry current gen MBT and other heavy armor from the very beginning, it was exclusively military, where as the Il-76 was initially designed to be a commercial cargo plane/passenger combi that can operate at low grade airports, and could at most carry a T72, hence the narrower body. Again it is about the purpose, the user requirements, not the age.
