I don't get the claim about it being "impossible" to shoot it down while hypersonic, either.

So maybe it's high enough that you don't have any interceptor missile capable of reaching that altitude... but if you had one, that hypersonic ball of plasma is not "hyperluminic", all that radio noise is going to light up on any radar like a beacon. Sounds like it should be easy to predict its trajectory, particularly knowing that it can't maneuver much at hypersonic speeds, so it should be even easier to plot an intercept course.

It may by impossible to shoot it down from behind, or from a plane right underneath that doesn't have hypersonic interceptor missiles, but from any position in front of the enemy missile... you could float a balloon onto its path, and hit it.

Also, there is lasers. They may not be great as an offensive weapon, or too easy to mount onto a plane, and need several seconds to burn an incoming missile to a crisp... but they do work at the speed of light, can't beat that.