When you fire 600 missiles in TP III, but your success rate is less than 20% and of those 20%, you hardly hit anything of strategic value to the Israeli war machine, you lose your deterrence completely.
Even 3,000 missiles is a large stockpile for a middle power like Iran.
It had been stated, times and times again, that MRBMs are not meant to be taken as the main offensive tool in your military strategy. MRBMs with only inertial navigation and ring-laser gyroscopes will not be able to reach a CEP better than 50-100m. Iran needed satellite navigation but Iran's space program was halted in 2013. Another wonderful concession to get that damn JCPOA signed.
This is why global powers do not count on MRBMs for offense and still maintain large air forces. To equalize the capability of a modern air force like the IAF, I once calculated that Iran needed well over 50,000 MRBMs with satnav, and Iran never even got close to that number. And my assumption was that our success rate would be 50%. With 20% success rate, Iran needed over 100,000 MRBMs!