I completely agree with your analysis.
In our houses we tend to add moisture to the air in many ways over and above what comes in from outside. We do this by cooking, cleaning, washing and drying clothes . In older houses, without damp proof courses, moisture is also drawn up into the walls where it evaporates to further add moisture to the indoor air.
Yes, I totally agree with this.IMHO, best place to use a pump is a cold frosty high pressure day outdoors - or manage the vapour with dryers.