Great criticism. For me the main advantage of OBS is that it avoids false alarm so Launch-on-warning(LoW) can reliably work.
If anything, OBS creates more alarm in a crisis. They are very visible and kind of like Strategic bombers. You know they are there. You know they are armed with nukes. You can shoot them down but in doing so there will be a nuclear war. It will be a great tool in peacetime because it exerts pressure to the adversary. It will be a very bad idea to use them in a crisis. Think of it this way, during the Cuban missile crisis, JFK is suddenly ordering hundreds of American bombers to take off and start flying close to the USSR. Do you think it is provacative?
You know neither US nor CCCP actually run LoW doctrines, mainly because of the pressure of decision making.
There are more reasons other than pressure of decision making. To run LoW, you will need very good early warning systems, great command and control systems and most importantly, a nuclear deterrent that is NOT survivable. Think of it this way, if you are sure that your nuclear missiles can survive, why bother firing them in hurry? Let the strike land first, ensure that it is actually nuclear, take your time to update target locations before firing. Keep in mind that if there is an incoming first strike, the adversary has most likely evacuated their population and military assets. They also have a smaller nuclear arsenal now. You may as well take advantage of it and wage nuclear war over a long time span.
Currently, the US is confident that its nuclear deterrent is survivable because its SSBN fleet is spread out and quiet. China is confident about its nuclear deterrent as well because it is difficult to hunt down all TELs in rapid succession. There is no point in running LoW because losing the silos do not translate to losing one's entire nuclear arsenal.
At the same time, without the fear of false alarm triggered war, China can deploy a fully automatic launching system with short range alarm(which should be effective for stealthy targets)and that would ban any B21/LRSO first strike.
Like Perimeter/Dead Hand? I don't think it is necessary. If the short-range warning systems detect incoming stealth bombers, the crew in the silos can launch with proper authorization. As long as the silos are manned 24/7, I don't think there is any issue in that.