> IMO, the regime is not as much worried about Israel as it is about the US.

The Islamic Regime is not a normal rational actor, their opposition to Israel is driven primarily by their ideology.

> Just compare the number of missiles and drones they shot at Gulf countries vs Israel.

This is probably more just a matter of Iran having more short range weapons than long range weapons, Israel is a long range target that much of their weapons will be unable to reach.