This statement of yours:
"Therefore, we would expect that the concentration of CO2 varies slowly and smoothly over both location and time. This being the case, the CO2 "control knob" effect (or equivalently the Clausius-Clapeyron equation) would constrain H2O vapor to also be well-mixed and slowly varying over location and time."
This is nonsense. Perhaps you're confused by the "control knob" phrasing. If so, just ignore it. It's very hard to understand what your point is, but I think it may be this: you think that for CO2 to be a "control knob" that it should overwhelm every other factor that determines water vapor distribution--for example, latitude, or proximity to bodies of water. That may be true on Venus, where the concentration of CO2 is high, but it isn't on Earth, things like solar insolation matter here. That doesn't mean that CO2 doesn't contribute, it does. It raises temperature and higher temperature means more water vapor.
EDIT: "Progressive Activist" may be an activist, but they are certainly not progressive. It is a false flag posting from someone that blocks me.