We don't really know how many people are doing Aminon, but if we assume it's a pretty small % (I know it is amongst the people I talk to) then...who exactly is going to subscribe (or stay subscribed) specifically because of the monthly Aminon RoE?
-People who are already grinding Aminon regularly? They're...already grinding Aminon regularly
-People who can't do Aminon don't care
-People who aren't even started with Sortie yet, don't care
-People who quit in the past are...going to re-subscribe now...?
IDK, I feel like Sortie is a grind and that's all there is to it. If you do 1 Sortie/month just to get the +2 earring from Aminon, you're not going to get much benefit out of it. To truly be able to benefit from Sortie you need to keep at it regularly and kill lots of bosses.
OTOH, people who get the earring they want from the RoE might be
slightly more inclined to say "*** it, I got my prime, I got my earring, I'm done."
I'd say neutral, possibly slightly net-negative. You aren't going to change the minds of anyone who's not ready to fight Aminon or those who don't want to grind Sortie, and those who want to grind Sortie are already grinding Sortie.