Brother. I agree with much of your post, however I disagree when you state that the 300,000 member increase in 1973 (74?)was due to dropping "unproductive" studies.
There has LONG been a correlation between groups setting predictions and rapid increase in growth.
I experienced this personally in a group called "Planetary Activation Organization" 6 years back. A Date was set for the return of "space brothers" to terra (earth)to lead use into 4th dimensional utopia, and the movement exploded with growth.
Witnesses reading this may scoff, but growth and prediction are closely intertwined.
Interestingly last week I was listening to a Fred Franz speech on what I call the "Eve extension" regarding 1975. We might have to wait a while past 1975 to allow the time between thr creation of Adam, and the creation of eve to elapse. This was a major speech at the time explaining the WTBTS predictive 1975 failure, anyway, the very next talk on the program after Fred finished mumbling, was Nathan Knorr.
He spoke about the GROWTH that took place during the org from 69 to 74. It was massive. The fact is, predictions set peoples zeal and hopes afire. The fact that the predictions, later, fail to materialize, seems hardly to matter.
If you want to start a religious movement...set a prediction. The method is well proven.