Appreciate the detail. I'm not sure I see the conclusion as obvious though; if a 2kg weapon is going Mach 20 (as the weapon in the OP apparently does), with 1kg of that being TNT, then the explosives only provided 20% of the energy (rounding to the nearest 10% to make the example clearer). If you just lobbed the same 1kg weapon at Mach 20 then you'd have halved the weight, and reduced the energy to 40%. Presumably lower weight means easier to maneuver (more agile for intercepting or avoiding countermeasures, depending on what you're trying to hit).

It seems like around Mach 10-20 is where the tradeoff could become non-obvious, depending on how much you value weighing less?

When close to the ground, something flying at Mach 10-20 would either be deccelerated very quickly to much lower speeds, if flying passively, or require a very large mass of fuel to maintain the speed.

Moreover, it would be hard to avoid being partially vaporized before reaching the target. So hitting something at Mach 10-20 seems much more difficult than filling the missile with explosives and detonating it.

Weapons based on kinetic energy alone seem practical only against satellites or against targets that fly in the upper atmosphere.

Per OP:

> The U.S. Air Force said on Monday it had conducted a successful test of a hypersonic weapon, which flew at five times the speed of sound.

But to your question:

> around Mach 10-20 is where the tradeoff could become non-obvious, depending on how much you value weighing less?

The same logic holds at mach 5-8 (ie current hypersonics), which is why they’re being developed:

You want a weapon that can surprise, evade, or penetrate better — even if that’s less destructive overall.