It would seem uniform ablation would be difficult.
Yes, uniform ablation is hard to get. If you ever have the chance to look at an old Apollo capsule after reentry, the heat shield looks like the end of a cigar.
I don’t know what they are using to minimize heat transfer. At Mach 6, the temperature of the air over the missile will be ~4,000 deg F, so there are some materials that would slowly ablate at these temperatures, which would reduce the surface roughness.
I really can’t speculate too much more at this point, but from what I know, I think that the speed is not ‘fake news’. As for being “unstoppable”, it may be for the British navy.