Grow up kid most modern Israel Iron dome can't stop all third grade Hama's rockets our ballistic and cruise missiles are far far more advanced so you would be shocked what we do during war.
You can't compare the working princple of Iron Dome with S400. The similiarities of both system ends in being air defence system. Iron Dome is made to counter the short range rockets and shells. Now to do this they does use Tamir missile which does have an electro optical sensor to detect target. In simple language it does scan for any change in light while flying toward the target. The ground based radar used by the system does calculate the approximate flight path of the projectile and it depends on its optical sensor to detect a fast moving projectile and once it is detected corrects its flight path to intercept it. In itself the seeker is bit primitive in working principle but a great way to intercept a small fast moving target like Rocket or a artillery Shell.
But S400 is a extremely long range to medium range Air defence system. It is made to target larger targets like BM, CM and primarily Aircrafts. Now the working principle of the Missiles used by the system is that they does use Active Radar Homing to pinpoint the target. The ground based radar of the system detects the target at extreme range and the missiles does use active homing in flight to detect the target. In short it does see its target at a long distance unlike the Electro-Optical seeker of Iron Dome which does it at a short range. So S400 is more efficient at intercepting large targets at distance unlike Iron Dome which does works for short range targets.
As such S400 is much capable system in targeting CM and fighters in its flight path and BM in its ascend.