It has around 42-77% success rate according to Ukraine themselves against specifically Iskander 9M723 and KN-23.

And your comment makes 0 sense considering S-400 was more designed against aircrafts and cruise missiles than ballistic missiles.

And that success rate comes after significant improvements to the Russian weapons and finesse. They were much less effective early in the war.

Cat and mouse is always a factor in war. The patriot wasn't very good when it was first introduced and took some refining to become the gold standard, which it still is.

It still works very well against planes too, reaching out and downing EWACS aircraft at the edge of it's range.

They were neither designed nor expected to have 100% defense rate, but 50% is lower than expected. 75% isn't great either.