Where are you taking your definition of hypersonic from? In aerospace subjects I've always used the threshold of mach 5, and a quick Google search confirms it, but maybe there are other standards that I'm not familiar with.

Russia launched 776 iskander missiles, according to Ukraine (idk if they would benefit from lying on this number, but it's probably in the same order of magnitude as the true number), but i can't find any reputable source stating that Ukraine can reliable intercept any significant number of those missiles (you are stating a 50/70% success rate, stopping some 400 missiles has to leave some indisputable proofs).

I'm not trying to give any opinion on Russia's use of missiles, i just think that underestimating the level of the Russian military technology is not something that will help us, in a war industrial might is a lot more important than the specification of a rocket (if you can't produce them, they won't have an impact anyway), and Russia proved to be extremely underwhelming in that aspect, but a nuclear warhead needs just one missile to do unimaginable damage...