Looking at the first table, the vaccinated cohort was obviously WAY less healthy to begin with. As expected; sick people were more inclined to protect themselves. Especially with the cutoff for inclusion being May 2021, presumably before younger, healthier people were being vaccinated.
Am I missing something in the methods that would control for this or... is it just that dumb?
Not sure about that. While there is a small bias, I'm not sure it sufficient to significantly nudge the result. For example, hypertension comorbidity is 262,659 / 842,974 in vax vs. 207,862 / 842,974 in unvax.
I'm not sure I'd call that hypertension difference small, and it's by far not the largest difference. There's ~30% more diabetes in the vaccinated cohort. 2x the rate of kidney failure.
Am I missing something in the methods that would control for this or... is it just that dumb?