Thanks for taking the time and thought for putting this together. Over the past few years this or similar reasoning has been discussed here. It is a difficult problem for several reasons.
One issue is that we have some actual data that is either published or observed and reported on, for instance: Number of baptisms, number of average publishers, number of peak publishers, Memorial attendance, attendance at conventions, the average mortality rate in a country. But other data is either assumed or only reported on incompletely, for instance the number disfellowshipped, the number of faders/ returners, the number of immigrants/emigrants between countries.
All in all it is a difficult math problem to try to explain how the WT can have positive growth in its published figures, yet every other measure we look at is in steep decline.
Getting back to the original post observation about the number of baptized as a percent of the attendees at a convention, the ratio has been running about 0.3% to 0.5% for last few years. As a comparison, I have an old assembly program from a big convention in Detroit in 1973 where the ratio was about 2.5%. I posted screenshots of it once on this site but cannot seem to locate it right now.