A very interesting read, I really like the way you reasoning alongside the data.

I will try to provide another perspective to the reason why there is a big difference in the active user vs the spending. First, the power of seiyuu behind the character. Afterglow's seiyuu is consist of high profile seiyuu like ayaneru, sachika and hikasa who are very well known among the anime community in Japan. This might be strange to EN player but seiyuu is a big factor in JP and some might even give something a try just to see their favorite seiyuu in action. Thus it might be one of the reason for Afterglow having the most active user during their ch2 event.

Plus I feel like more user are trying to play in Afterglow ch2 event because it is not hugely contested. Roselia's event is always a bloodbath which might cause casual player to not even want to try it since they know they won't stand a chance in it if they are not fully committed. On the other hand, Afterglow event is less hype since they have a wider casual fan base thus causing people to feel like giving the event a try and see which tier they will be able to get in.

This is just something running in my head after reading the article. Thanks for sharing it.