Let's suppose a cruise missile flies for 200 KM before entring enemy territory, to reach its target. It will have more success rate since it has flown for 8% of its defined capability. This distance will be increased to 2000 KM if enemy's A2/AD capability exceeds more than 1800 KM. Iranian long range radars stationed in Persian Gulf will have more time to detect and counter it.Not sure how you reached that conclusion. Accuracy and success rate based on what?
Let's make an other assumption which is far from reality, USA has developed hypersonic CMs for its naval fleet. There is however no evidence that USA has such capability but even if true the longest range of an scramjet powered hypersonic cruise missile at the moment doesn't exceed more than 2000 KM.
The longest range of Tomahawk missiles are 2500 KM ones. The missile has to Fly for 2000 KM from the mother ship/base in order to hit its target, it means 80% of its fuel is wasted to avoid Iranian A2/AD capability. In this scenario the success rate of a cruise missile will be at its lowest.