Earlier quoted context omitted.
The new thing is trying to go hypersonic in the atmosphere for more than a couple minutes so you can use it for lift. But either there's too much heat or not enough lift.
No, this is in fact not categorically new. MaRV and related demonstrated 60 G pull up to horizontal glide maneuvers. The technology of a HGV and a maneuverable re-entry vehicle are essentially the same. The main reason for talking about "hypersonics" as a separate category today is to emphasize flight profiles that would not be interpreted as nuclear strikes.
As I understand it, it's not about “not being interpreted as nuclear strike” — since almost every Russian missile (including anti-ship missiles like Kh22 and the likes) could potentially carry a nuclear warhead, they explicitly don't care about the ambiguity, while the Western doctrine is diametrically opposite, explicitly aiming for as little ambiguity as possible to keep the escalation risk low. And your interpretation basically goes against both doctrines. — But more about keeping a low trajectory so that the missile stays below the early-warning radar horizon for most of its flight, striking without warning, where a ballistic missile gets within the LOS of radars quite early due to its trajectory.