I think it's a product of the game getting more popular... but if there's something I remember fondly, it's the fanart of Athena neglecting Eric.
I think what really boosts Arcadions popularity is the simple upfront personalities and easier to draw designs.
I recall a mountain of memes surrounding the 'Gaslight, Gatekeep, Girlboss' Athena.
https://pbs.twimg.com/media/FyXcM1pXgAEQ04z.jpg
I don't think Mide was as hugely popular but Alpha and Omega, Gaia, Eric, and Hesperos had their fair share of fan art and cosplays and Athena was all over the place. So this is pretty par for the course.
We got Alpha on the Omega raids and he's still roaming around Eorzea with the mini Omega robot. Every time i see them in the world i get the biggest of the smiles.
I think most, if not all, of the past raid exclusive characters have been popular at one point. Alpha and Omega, Gaia, Eric, Hesperos, Hegemone, Agdistis, Hephaistos, Themis and Lahabrea [depending on how technical you want to be with "exclusive" given we got to see their true forms in their raid series], and Athena all had their moments of being popular. Even Mide I am sure was popular back in Heavensward, even if she isn't mentioned at all anymore and forgotten to time. So this really is just par for the course.
https://imgur.com/kx4vD62.gif
I'm hoping they go back to my daughters sometime in the future. A nice small time jump would also be kinda fun for them.
https://i.redd.it/1qzol8ejzbpa1.jpg
Pandaemonium characters are very popular. They still are. You can find plenty of new artwork of them at least weekly.
As much as I like Honey B. Lovely, I think she's going to go the way of the dodo just like all of the Nophica love. She's great, but there just isn't enough to hold onto for a long time.
I don't see much Wicked Thunder stuff, but maybe that's just the algorithm doing algorithm things.