Yeah, I'm in the skeptical bandwagon on this. The vax rate (doses/day) *is* ticking up as a result of the mandates for sure - without the mandates, the rate would continue to taper to almost nothing. However, I don't think that uptick (from a relatively small baseline of just 650K shots per day) is responsible for the dramatic reduction in hospitalizations and presumed future decrease in deaths that we'll be seeing.
I'm also not convinced that a significant enough number of unvaccinated people modify their behaviors (masking, distancing) in the face of spiking COVID cases to arrest and then reverse the growth rate. At this point, most unvaccinated people are pretty hard-core deniers/freedom-over-responsibility types - just go check out your local school board meetings, if the public is even still allowed at yours.
My suspicion is that there's an inherent variation in susceptibility based on the complex interactions between virus and body chemistry. Each variant burns extremely quickly through the people who happen to be highly susceptible, that sub-population achieves "herd immunity" to that variant, and then the case rate drops back to the rate dictated by the less-susceptible population. I have no evidence for this other than a lack of correlation with other effects that could be causing the wild swings in numbers. We've had peaks in different seasons, on holidays and not, with a decently vaccinated population and not, etc.
My county in Florida went from 655 new cases/day for the week ending August 26 to just 172 cases/day for the week ending Sept 30. The population did not get 4x more vaccinated, 4x more mask-compliant, or 4x anything else in that span. (yes, yes, I understand non-linearity, I promise.)
Bottom line: It's the viruses' world - we just (try) to live in it.