I don't have the source handy so you'll have to "dude, trust me" on this but XY did have sub-legendaries: Mega Evolutions.
No, seriously. Apparently the developers internally considered Megas XY's equivalent to sub-legendaries. My buddy ol chum
Hematite could tell you more on this but with this knowledge in mind suddenly SO many things about how they were handled start to make sense.
Oh! I know it was a while ago, but if it helps, I was just referring to this when I said that:
https://bulbanews.bulbagarden.net/wiki/Nintendo_Dream_interview_reveals_new_mechanic_changes
The power-up of Mega Evolved Pokémon is meant to elevate them to the class of legendary Pokémon, hence the restriction of only one Pokémon being allowed to hold a Mega Stone during battles.
It was my interpretation of this that Kalos didn't have any traditional minor Legendaries because the Megas were already acting in that capacity, and that's also why most of them were postgame and so few of them were used by NPCs;
it just happened that, because X and Y lean so strongly on fanservice all around, they basically thought it would be more fun if their would-be "minor Legendaries" were all "evolutions" of old Pokémon this time around (chosen "based on three points: visual looks, popularity and game balance"). Then they made so many of them that they added a GS Cup-style limitation to keep from crowding out the regular Pokémon (I mean, they'd never made 31 Legendaries at once before--), and the "mechanic" itself wasn't really meant to be much more than the cleanest execution of that.
For what it's worth, even if it can't be said that Megas were conceived as an
explicit stand-in for minor Legendaries, the fact that a) they were compared to them from a competitive point of view and b) this comparison was given as the primary reason they chose to limit them to one per team all but confirms they were still competing with them for "space," as it were.
Maybe they didn't make "real" minor Legendaries because Megas were the minor Legendaries in their eyes all along,
or maybe they didn't make "real" minor Legendaries because - knowing that they were already pushing it with 28 Megas and that they even felt the need to introduce this one-per-team limit to limit their impact - it would be self-defeating to make even more Legendary-tier Pokémon that didn't follow that limitation.
Either way, the reason there were no other minor Legendaries seemingly does just boil down to "they thought that would be too many because of Megas."
Obviously they're kinda occupying an in-between state where they're not
really Legendaries, but I found it useful to compare them to stuff like Ultra Beasts and Paradoxes if anything.
- They're all groups of technically-not-quite-Legendaries, but they still fill mechanical roles that are openly based on and adjacent to Legendaries, especially competitively, and they have in-game lore and campaign roles that tie them to the game mascots and all that;
- they're more numerous and diverse than most actual Legendary groups;
- each one relies on a distinct unifying mechanic (Mega Stones, Beast Boost, Proto/Quark/Booster Energy) and a distinct stat scheme (+100 BST, 570 BST made of prime numbers, 570/590/670 BST made of evens for Future/odds for Ancient) to set itself apart as a group, since there are too many to do the usual trio and quartet tropes of "one shared type" or "stats that just rearrange the same numbers;"
- a few of them are encountered during each campaign, but the floodgates are opened so you can obtain them all for yourself in the postgame;
- and so on...
That kind of thing is what I mean!
Megas and Paradoxes are both, even more specifically, about as close as you can get to "Legendary-tier variants" of preexisting Pokémon, just that one is considered a form change and the other is its own species,
and a lot of the specifics of how Paradoxes were handled feel to me like a direct attempt at responding to the most common criticisms of Megas in VGC and giving a second try at almost the same idea. (They
genuinely nailed it, for what it's worth! which makes me wonder if they might take anything away from that and rework the mechanical limits of Megas at all, now that they're revisiting them anyway.)
But yeah, when I brought up that interview with Dramps, I was basically trying to make the case that Megas were something much more functionally similar to Ultra Beasts and (especially) Paradoxes than to any of the so-called "generational gimmicks" / Z-Moves, Dynamax and Terastal; I was arguing that they at least
should be treated like just another set of minor Legendaries.
Like, I'm sure they wouldn't belong in every game
(which is also how I feel about true Legendaries... please stop putting every Legendary in every game it's getting ridiculous), but it just makes more sense to me to put them in rotation with the others, just like we got Ultra Beasts mixed in with the Legendary spam last Gen despite them
totally definitely surely not being Legendaries, and just like I'm sure we can expect to see the Paradoxes brought back in a non-Paldea region for random postgame/competitive use once in a while, with or without getting any new ones.
I'm not 100% sure if Game Freak necessarily sees them that way, but
I stand by it being the best way to look at them, if nothing else!
I definitely consider them Gen VI's minor Legendaries in everything but name, and I really wish more people would see them that way;
I think choosing to regard them more like Paradoxes and treating them as their own Pokémon that are just consciously built on a relationship to old ones (and less like a mechanic that could be made universal / should be held to the same standards as Z-Moves, Dynamax or Terastal or like simple "buffs" or "fixes" for their base forms) would help a lot of people to move past some specific criticisms of Mega Evolution that I don't agree with and get a better sense of what they were actually trying to do.
Uh, I could probably say more about this or explain myself better, but I am getting a bit off-topic and a bit tired right now, so I will stop myself for now--
edit: okay, maybe I'm just out of it right now, but I used way too many italics in this post and it was driving me crazy on rereading it--
uh, hopefully this is a little more readable!