I agree with your point in the near term, but beyond that I disagree with you about the effectiveness of submarines for maintaining the second strike deterrent

I agree with your point in the near term, but beyond that I disagree with you about the effectiveness of submarines for maintaining the second strike deterrent for two reasons. First, there is some threshold amount of off-Earth allied population that will undermine and make irrelevant the SLBM deterrent. In the extreme case, consider a Martian opponent. Second, there is a gamble that a first strike against military targets won’t provoke a return strike against the civilian population. In this case, a restrained first strike that takes out key submarine docks could degrade the advantage provided by Boomers. A limited attack on that kind of infrastructure is hard to pull off, but an asteroid strike might be one of the few ways that it could be done with sufficient plausible deniability. Gravity-based kinetic weapons will force a rethinking of nuclear MAD — the history of war consistently shows that expensive hardened fixed positions are eventually made into vulnerable death traps through cheap technology.