Maybe, but that's not actually relevant. The problem wasn't whether the Soviets would use their SLBMs to attack missile bases in such a way that launch-on-warning could not be guaranteed, it was whether they could, especially since in context the Air Force was trying to develop a system that might be in service for several decades (as Minuteman III would have been by the point Peacekeeper or Midgetman could be deployed) and it was very plausible that the Soviets might upgrade their SLBMs by then. I mean, the Peacekeeper survivability studies also considered the Soviets smuggling in spetsnaz teams to physically attack missiles, especially in a rail-mobile or road-mobile road. Compared to that, depressed SLBM trajectories seem pretty reasonable!
In any case, the result was that the Air Force didn't consider launch-on-warning a viable method of ensuring the survivability of the ICBM force in the face of a hostile first strike by the 1980s, or at least not one that could be counted on indefinitely. So they cast around for other methods, including airborne ICBM launchers that could stay on constant patrol and therefore would be much more survivable (however had other problems which led them to select ground-mobile systems instead).