It'd take forever to reply, and to be honest, I find most of what you said ludicrous.
Uh-huh, lets begin...
- Mega Evolutions are all similar to Form Changes. They're all major differences period. No palette swaps exist. Saying it could be one is severely grasping at straws just to assert something that zero evidence supports.
And in the same sense, "zero evidence" supports them being forme changes, as it goes against what GF does when promoting forms or Mega Evolutions. They've never called things like Deerling Spring forme a "new Pokémon," but they have done so for things like MegaMewtwo Y and Black/White Kyurem, so it's highly unlikely that they'd do so now.
So the problem here is that no matter how you look at it, these do not fit into the criteria brought up by their predecessors.
- The Ancient Digimon are quite a bit different. First off, they didn't automatically come from the two Spirit of [Element]. For instance, AncientGreymon can come from Agunimon or MetalGreymon as a proper Ancient Evolution. Besides that, they are not a true "earlier form" like Kyurem's was. The thing is, Pokemon and Digimon work very very differently. Devolution is something too different to compare to Pokemon's. A devolution is just returning to a lower form, not combining with another Mon to become a lower form. It's not even possible. Devolutions are also extremely common in Digimon and they can evolve/devolve on a whim if teamed up with a Digidestined/Tamer.(Tamer is also an official term for those who train Digimon as is, a Digidestined is the official term for those with a Digivice. Generals in Fusion are the same as Tamers. I just wanted to note that a bit. I know it's not that related, but it should clear up some confusion about the differences)
No, they were. The Ancient Digimon are the original forms in a sense for the spirits, they are the Digimon that those spirits gained their abilities from by splitting off their power. When brought together, they can reform the original Digimon by starting to take the steps to it, they are one potential evolution possibility for them, but an evolution that they can do nonetheless.
And you missed the point of that, those Digimon being reformed were not classified as "Devolutions," officially they're evolutions. Similar to that, Kyurem-B/W has never been classified as a "Devolution," because in the same sense it's ascending to a more powerful form via recombining its parts.
In short, it's not a devolution to recombine to make a more powerful form, that has not been classified as such.
- Mega Aerodactyl being its true form is a theory. Likewise, using that theory as proof doesn't help, since we don't know if it's even true. Likewise, Aerodactyl becoming its current form is likely because it was revived incorrectly. There's theories that Kabutops is what happens when a Kabuto attains its form before it was fossilized. Basically, they could be the same as thing as what Mega Aerodactyl is, returning to their ancient forms.(and it would be funny if Ancient Devolution became official for the other Fossils).
You brought up the theory, I just turned it on its head and shown how it could be used to support the other side.
Also, the Kabutops theory isn't supported by canon at all, that's completely fan-made at this point.
- Ancient Devolution and Mega Evolution are specifically said in the same magazine and treated as separate things. It doesn't make sense to say they're the same thing when they have nothing in common anyway. It's unlikely it's a Mega Evolution when they called it something different, showed no signs it had to deal with Mega Stones, and mentions more than one Mega in the Magazine's articles about it. It doesn't add up. If it was a Mega Evolution, they would've just said it as is.
You're completely missing the point. I'm saying that they draw from Mega Evolutions while being their own thing, essentially a little deviation to make them standout from the current mechanic while still being a spiritual successor to it. We know that they're different already, but we don't know nearly enough to say that they're completely disassociated from Mega Evolutions.
Also, they rarely expand on Forms when first revealed, MegaMewtwo Y and Black/White Kyurem did not get any expansion on what they were until GF felt ready to do so. They could be doing the same here, particularly since we know little about them.