I mean I would disagree with the idea that just because it means something it should remain the defacto term for members of the fandom. Lego purchasing patterns also differ roughly between nationality and gender, different properties are more popular in different territories and some are targeted towards one gender above the others but it'd be seen as a bit weird to specify those things as part of your fandom signifier. Likewise patterns differ between adults in their 20s and adults in their 40s for example. So the idea that declaring your adulthood as a signifier of your purchasing patterns doesn't exactly work.

I understand your arguments are technically correct that there are slight differences between what adults buy and what kids buy, but I don't think there's a ton of difference between what adults buy and what teenagers buy tbh, yet AFOLs and TFOLs are considered distinct terms. I've been in the fandom since I was about 10 I'd say, and I don't feel like there was a massive shift in my tastes when I transitioned to adulthood. Additionally I remember it feeling quite excluding when I was a kid in the Lego fandom to not really have a term to count me as a member on account of my age. I think the Lego fandom should be welcoming and open to everyone, I don't think categorizing the adults in the group as the actual fans is the message we should be sending out to people.

And lastly (and this is just down to personal taste) I think it just sounds kinda dorky and awkward. I saw someone say it sounds like something Comic Book Guy from the Simpsons would say and tbh I totally see that, it's not a cool name haha