"Even if you extend the offensive radius to 115 miles, you are still limited by a slow moving platform that must move into the teeth of shore-based missile and air defenses."
If your offensive capabilities are out of the range of shore based defenses then you hit them before they can hit you. The offensive capability of BB is not just limited to its guns but its missiles and its excorts capabilities. You are making an assumption that this platform would be the sole attacking platform in a littoral operation. The defenses you are speaking about would probably long be destroyed by both cruise missile and air attack like any other fortified area. Our armed forces destroyed Sadam's Fortress Kuwait in a systematic fashion utilizing multiple systems. I don't see that changing much today.
No, but I am making the assumption that the BB needs to operate in a fairly low-intensity 21st Century enviornment.
For example, current thinking would position carrier battle groups to the east of Taiwan in any defense of Taiwan and any entry into the Straights of Taiwan in wartime is considered extremely risky.
So, as I understand the reasoning, the 21st Century use of the BB would be as a gun platform in a low-intensity enviornment where the enemy missile defenses and airpower have been neutralized.
In addition, its use would be limited to targets far away from any town or urban area since it is guaranteed that any shell landing within 25 miles of a populated area would score a direct hit on a "Hospital" or "Orpahage" or "Baby Milk Factory" and the footage of mangled children (which CNN keeps stock footage of ready to transmit at 30 seconds notice) would be all over the World's TV screens by dinner time.
So, it seems to me that, in the 21st Century, using the BB for littoral bombardment is like using a glass sledgehammer to kill flies in a china shop.