We spent the whole Cold war tremendously overestimating the Soviet Union's military prowess.
“I’m sure its a decent system, but if they are so good, why do we and the Israelis blow through them so easily?”
Thanks to our Wag the Dog president, Russia is considering its first foreign sale of the S-400 system, to China.
So, unless we and the Israelis have been attacking Russia itself, we have never tried engaging the S-400 system. You may want to research it.
As to their older systems...since we NEVER engaged their best weapons, only the ones they exported. It’s also worth noting the S-400 system was developed using Western technology, as it was developed after the Soviet Union broke up and export controls were greatly loosened.