This does not weaken the argument, which is about proportions and rates, not about absolute numbers. The number of 18-year-old graduate recruits increasing implies nothing about their recruitment rate, which could have increased, decreased, or stayed the same.

This does not weaken the argument because who is able to operate military technology is unrelated to who the military is able to recruit. We also don’t know how many people are needed to operate the tech: maybe it’s just a few, so they could still mostly recruit dropouts.

This weakens the argument, because it rebuts the author’s assumption that the observed correlation implied a causal link. This instead shows us that the increased recruitment rate was not dependent on recruiting more dropouts, but rather more graduates.

This does not weaken the argument, because the domain of the argument is limited to who the republic’s military is recruiting. Whatever education people pursue after they have already been recruited is irrelevant.

This does not weaken the argument, because the argument is purely about 18-year-old recruits, who we already know are usually either high school graduates or high school dropouts. Recruits who join later, after several years of college, are outside the argument’s domain.