Here's a question you may not have thought about: Who was in Lumiose City for the parade at the end of the game?
(...)
Of course, it would be the masked heroes hiding in plain sight, being the only ones to use the title "defenders of Kalos" in the story, and being the only other people who are actually said to be battling Team Flare in the climax. Overall I would say that Sina and Dexio were the real defenders of Kalos on the stage in the ending of XY, but to avoid exposing their secret identities they just volunteered Trevor and Tierno to get the attention instead.
Eh, I think you're overthinking it. Why were Trevor and Tierno included even though they didn't do much? Because they were still there providing some support, even if by their own admission that Dexio & Sina were doing most of the heavy lifting as the "Defenders of Kalos". Had the parade also included the "Defenders", it would be the seven of them getting awards. But since Dexio & Sina were playing superhero, they rather not have their secret identity "revealed" so decided not to be awarded on stage (though Sycamore may have given them medals in private and/or included somewhere that the Defenders of Kalos were also present helping out in the official report).
I believe that Gardevoir was retconned in ORAS to be a tailor-fitted common team pick.
Was it a retcon? I mean, yeah, Dexnav made it easier to find, but you can still find a Ralts on Route 102. Sure, it's a rare encounter, but like any rare Pokemon that just means you need to grind encounters until you finally find one. So I still think Ralts is as much as a "common" team pick as it was in Gen III, it just now comes with the bonus of having a Mega Evolution. Also Wally's ace changing from Gardevoir to Gallade I think more had to do with Diantha's ace being Mega Gardevoir. So instead of keeping the "original" RSE story of Wally where Gardevoir represents a guardian angel figure, Wally's story becomes one where he overcomes his shortcomings and becomes a strong & capable trainer with Gallade representing the more "warrior"-like change.
Somewhat unrelated but I was stunned when seeing that Ogrepon's japanese name was also Ogrepon; I thought for sure it was going to be "onipon" and that localization was falling on the weird thing of "all oni must become ogre"
In many Japanese high fantasy series, Oni are usually related to Ogres, with Oni often being stronger and more advanced/evolved than Ogres are.
I think it's actually intentional they went with "ogre" instead of "oni", and not for (completely) the reason you're thinking.
Now note that, when it comes to names of Legendaries and Mythicals, GF nowadays likes to have most of the names be the same at least between the Japanese and English translation. If they have a different name between Japanese and English there's usually a reason.
Now, for the Momotaro Trio, due to what GF wanted to do with the names it made sense to have different localized names. Not sure how much part of their design/lore it's going to link to, but I imagine the Dog relating to approval, the Pheasant to fortune, and the Monkey to improvement is part of the overall design thus them wanting it to be represented in the name (and in some form of archaic style; Japan (and I imagine Chinese and Korean) it's an old way of saying the animal's name, English/Spanish/Italian using old/outdated English slang or words, French using Greek/Latin words for the animal, and German using all foreign words). And kudos to the English translators, notably for Okidogi and Munkidori, I'm not sure if I would have even thought to do that!
As for Ogrepon, as you see GF decided to keep the name the same between Japanese and English. But still, why not use "oni"? With how connected the world is nowadays, most people know that Oni are a Yokai (which most people know means "Japanese mythical monster"), and a lot of Pokemon are based on Yokai because Pokemon is a Japanese franchise. Well, something that
Nokocchi noted reminded me of something. Fun fact, what is the Ghost-type called in Japan? Answer: Ghost-type, as in the English word. Now, Japan does have its own word for "ghost":
Yurei. However, in general Japanese culture, a yurei is meant to be taken more seriously. Hence, GF deciding to refer to the Type using the English term which has a more wider interpretation which includes kid friendly ones like Casper. Going back to Ogerpon, note that it has the prefix "-pon", which is meant to indicate that it's supposed to "cute". Oni are usually depicted as ugly and gross, and while the same can be said of ogres, let's be honest, the first character you think of when you hear "ogre" is Shrek; a kid-friendly character who is meant to have a charming/cute grossness about him but is a good guy (flawed, but good). So, because they want to get across Ogerpon is meant to be a cute Pokemon, at least to the Japanese audience, they chose the mythical creature which as the more "kid-friendly" character connected to it.
Which isn't to say it won't have an "Oni Form", especially with it potentially having a mask gimmick. I can see it now, it's base form is "Masked Form" where its a silly little ogre guy, but when the mask comes off it changes into its "Oni Form" where is gets bigger, stronger, and scarier looking.
), a super form of an offensively inclined legendary(e.g. 
, or having a concept built around high offense with a clear drawback (e.g. 
). Mewtwo's 154 SpA on a base form with no stats below 90 or harmful abilities is still exceptional. Pretty much the only other thing in that group would be Xurkitree, though it still contends with all non-SpA stats being in the 70-90 range.
