You have an incorrect notion of how air defense is conducted.
What you need to ask is what targets were destroyed on the ground, not how many missiles got through.
In order to conserve ammunition, the SAM commander will allow some missiles to go through if the missile is targeting areas of no consequence or not of vital importance. For example, if an enemy missile's headed towards an empty hangar, the commander will let the enemy missile hit the target because rebuilding the hangar is cheaper than wasting an Arrow missile.
No, THAAD isn't better than what the Israelis operate. In fact, Trump wants to replicate Israeli missile defenses for America. Israel's defenses are far more strategic in nature, whereas THAAD has been designed for mobility and quick insertion into new areas. Both its radar and interceptor are inferior to the Arrow system. The Israeli system is a generation ahead, and India's is even more advanced.