One tidbit I would add about Regieleki: A major characteristic of the Information Age is the speed with which technology and information spreads and develops. What is Regieleki's greatest stat?Going to play devil's advocate here: Regieleki and Regidrago aren't as out of place as you think they are. For starters, you're taking the age thing too literally. Regieleki and Regidrago aren't based on the names of the ages, but the defining characteristics of those ages as a whole. The Dark Ages is a colloquial term for the Middles Ages, and what mythological creature started becoming really popular during the Middle Ages? The dragon. Regieleki, meanwhile, is most likely based on the Information Age, where technology began improving vastly. Usually technology is associated with metal, but there's already a Steel Regi, so GF went with the next best thing, the Electric type, which works due to these new technologies needing electricity to even be powered in the first place. It also makes sense that their material of origin isn't a solid and that they were "shoved into" the Regis's existing myth. They're extremely powerful beings who were sealed away and written out of the Regis's original lore due to their immense strength and the fear that they could hurt humans. And it makes sense that they have super-abilities instead of Clear Body. Their bodies aren't solid, so light can't reflect off of them. And once again, they're incredibly powerful and destructive, and Transistor/Dragon's Maw fits their lore. I will agree that it was dumb that the original three Regis didn't get new signature Abilities/moves when Eleki and Drago got them, but then again what would those sigs even be?
If there is one thing I do love about both Eleki/Drago and Enamoruseven if the latter's Incarnate design makes me want to gouge my eyes out with a Taco Bell sporkis that they are showing that GameFreak isn't afraid anymore to add new members to old Legendary groups. I hope they continue to do this for following Generations. They could make new Legendary beasts, new Swords of Justice... hell, they could even take Legendaries who aren't in a group like Heatran and make a new group for them!
...ok now I'm getting off topic, the TLDR is that Eleki/Drago and Enamorus both fit into their respective groups, Eleki and Drago are just weirder and wackier about it while Enamorus is more traditionaljust like the games they were introduced in! who would've thought?
I'm mostly popping in to say I hope some of these aspects make their way into main series at some point. Also I will die for Snail Goodra.
Apologies if the following spoiler theory has been discussed in previous pages
My personal theory for these is that the forms are meant to weaken them somehow. Compared to Giratina's Origin form which is much more natural and streamlined, these forms look so messy that it has to be by design. Palkia has no arms despite its Bipedal design using them for moves like Spacial Rend, and Dialga's throat looks blocked to the point it couldn't breathe, much less use Roar of Time.
My guess is that for whatever reason, the villain inflicted these on them so they would either be out of the way of their plan, or easier to control for it such as manipulating the two clans. The mishmash of Arceus traits might suggest they were Guinea Pigs for something said Antagonist plans to do to said Arceus and will be the Onus for the Endgame or the last fight/quest before actually being able to Catch Arceus at full Pokedex
My guess is that for whatever reason, the villain inflicted these on them so they would either be out of the way of their plan, or easier to control for it such as manipulating the two clans. The mishmash of Arceus traits might suggest they were Guinea Pigs for something said Antagonist plans to do to said Arceus and will be the Onus for the Endgame or the last fight/quest before actually being able to Catch Arceus at full Pokedex
