That would require a timeseries analysis and as far as I know, the data are not readily available. As you say, this is a static analysis and should be read as such. I.e. across all individuals who have reached are currently at the level of Friar, what is their total number of XP and what is their total number of writeups.

There is a huge danger in stats like these that people will confuse correlation with causation. These are descriptive statistics only.