The MX Missile was never necessary. I have no idea why it was developed. 12 Madison and Franklin class submarines were refitted with the Trident C4 SLBM from 1978 to 1982. A total of 192 Trident C4’s. Each one could carry 8 W76 (100 KT) warheads with a range of 4,000 nautical miles. The Trident C4 was also deployed on the new Ohio class submarines. By the end of 1986 we had 3,072 warheads deployed on 20 Trident submarines.
There was really no need for the MX.
I believe that it truly was time to modernize our land based missiles, although I would have preferred they be on mobile launchers, but I think we agreed in a treaty not to field such capabilities, but I don't remember for sure.