Heat and air resistance is not such a big challenge now with almost the whole world having its own IRBMs etc. You are raising an issue that was relevant and solved and then the world began building up on the basis of the building blocks already completed. HGVs are not some Kryptonian tech. Only the applications are special and the fact that it is a sweet technical solution to a lot of problems. And the fact that there is a great developmental path that the HGVs open up.
Experiments are essentially required for controlled flight or skipping along on the the upper atmosphere and hypersonic descent. Later on they will add propulsion and most likely there will not be any explosive warheads involved ever so they will require re-experimenting on the final maneuvers at sometime in future.
DF-ZF is meant for between 5-10 mach experiments.
India has carried out its own experiments at Mach 5 till date.
Size has nothing to do with the difficulties involved. China too can experiment right now with smaller HGV and India can do the same with larger ones too.
China is ahead in the race but not terribly so. India will cross the river when India reaches the river.
K-15 is a BGRV. Unitary warhead getting maneuvered into position at hypersonic velocities. As usual we are the 5th or 6th nation to do it. Which is what irks me too but its something I cannot avoid.
If you are interested in checking out what India is doing then you can refer the open source material.
https://en.wikipedia.org/wiki/Hypersonic_Flight_Experiment
https://en.wikipedia.org/wiki/RLV_Technology_Demonstration_Programme
This was a demonstration for a basic two-stage-to-orbit (TSTO) fully re-usable launch vehicle. Launched on 23 May, 2016.
Now this was hypersonic descent at a mere Mach 5 or about 1.2 kmps.
The following one demonstrated the upper atmosphere skipping maneuver at 5 kmps and achieving the correct re-entry position to finally enable the survival of crew, equipment (which obviously has military applications too). But is not about hypersonic descent.
https://en.wikipedia.org/wiki/Crew_Module_Atmospheric_Re-entry_Experiment
check out the full details of the flight. Notice at what parts of the trajectory it achieves the max velocity for the ranges involved. Esp. this portion:
Don't try to impose the superiority of the exotic middle kingdom tech here.