You missed the point. It's less a question of solvency than a question of predictability and neg bias. Nobody is questioning whether fiating Navy reserves into the Coast Guard would solve as an increase mechanism, because of course it would, but the issue of whether it is feasible as a real policy certainly is raised. It also opens a pandora's box of issues with competitive equity--the concern that allowing this means that the neg can take any person from any organization, be it government or not, and fiat them into the Coast Guard. Unless you are willing to defend that research burden, the solvency advocate criterion seems reasonable. Conversely if the aff has a squirrelly case, the neg's burden of solvency advocate scales back as well, ensuring a fair division of predictability. Your tolerance of counterplans seems myopic in the sense that the neg can just get away with too much.
This seems rather tripe in light of the fact that the counterplan is everything the affirmative does with the exception of a different solvency mechanism. I guess this isn't a PIC if agent CPs arent PICs either. The only legitimate argument that could be inferred is that, as an offset, it tests the affirmative's adherence to the resolution. However, as it does cause an increase within the Coast Guard, the offset refers only to not recruiting new people, not not increasing within the Coast Guard.
Of course politics links deal with increasing personnel within the Coast Guard. However, you've functionally conceded that no author will advocate that offsetting from Navy reserves would cost less political capital. You, as you admittedly pointed out, are left with analytics to piece the two together. Again, the issue of competitive equity is raised. Apart from training, there is no unique reason as to why Navy reserves are in the unique position to be of benefit to the Coast Guard. Reading politics with this "counterplan" takes a mile-wide leap of faith and just encourages the neg trying to pop the aff with a random, generic strategy that has no merit in a policy paradigm, something you submit to when offering a counterplan. As to the issue of wage inflation, the bar of a solvency advocate should once again be applied. Although the argument might be true in certain contexts, I don't believe that a generic piece of evidence that nowhere mentions the Navy, the Coast Guard, or the Navy and Coast Guard should be enough for you to consider this a legitimate net benefit.