關 is a compound of 𢇇, which represents threads or ropes binding the beam of a portal, 門 being a gate, it means "barrier, frontier pass, close, relation".
東 is traditionally thought to represent a sun rising behind Fusō, a mulberry tree in the far east where the sun originates according to Chinese mythology. It means East.
Together, in the context of Japanese history and the real-life region of Kantō, they represent the region east of the Sakone pass, the main tollgate between two historic economic centres of Japan, Edo and Kyoto. We can also interpret the name in the context of the Pokémon world as east of the Victory Road gate at Mt. Silver.
Johto = 城都
城 is a compound of 成, representing an axe with the handle to the right and the blade to the left, with the little half-square representing the border of a city, and 土, a lump of dirt representing earth, together they represent a castle or urbanity in general.
都 is a compound of 者, a sugarcane with its stems and a mouth, meaning to boil (original version of 煮, later borrowed to become a nominalising suffix), and 邑, a person kneeling outside of a city, together meaning a metropolis.
Together they represent Ecruteak, the traditional capital of Johto, and its iconic Tin Tower and Brass Tower.
Hoenn = 豐緣
豐 is a pot of plants 𠁳 on top of another pot 豆, representing fertility and abundance.¨
緣 is a compound of 彖, a pig with a prominent snout meaning "hog", and 糸, silk threads, together meaning the hem of a cloth, its edge. It semantically shifted to mean edges in general and eventually destiny, serendipity.
Together, it has been stated by Masuda to represent the serendipitous prosperity of humans and Pokémon, but we could also see it as representing the ideologies of Team Magma and Aqua, a destined land of abundant land or water.
In the Gen 1 Kanto games (IMO the only canon Kanto games) the following Pokemon are not used by any Trainers in the game. See pic related.
The Legendaries make sense, so we don't need to talk about those.
The Rival only uses Venusaur if you pick Squirtle, and many would argue this is the non-canon starter choice for Red. He uses Pidgeot in RGB but NOT in Yellow, which many would claim is the canon version due to Red's team in GSC. He uses Eevee and its Eeveelutions in Yellow, but we have never gotten any clue as to which form is canon. Outside of this, no other trainer in the game uses these Pokemon.
The top rows of pic related are Pokemon that NO NPC uses in-game.
But why?
What’s up with Golem? Alakazam, Machamp and Gengar are all used by other trainers, so everyone in Kanto knows that trade evolution is a thing. You mean to tell me that not a single person has evolved their Graveler this way? Hm...
Clefairy is rare, sure, but trainers do use Clefairy + Nidoqueen, Nidoking, and Wigglytuff, so Moon Stone evolution is clearly known. That excuse fails.
There is a trainer outside of Celadon that has a Poliwrath, but for all we know this might be a non-battling Poliwrath. Outside of him, there are no trainers with a Poliwrath.
Porygon is available to all in the Game Corner, though that is a hard one to obtain so understandable.
There's a girl in Mt. Moon that tells you she's looking for fossils she's heard about. Then you get either the Dome Fossil or Helix Fossil later. There is no evidence to suggest that these are the ONLY fossils in the cave, and the Cinnabar Lab is known for restoring fossils, so other trainers would surely have the fossil Pokemon as well?
There being two Snorlax confirms that more Snorlax exist, so no reason there either.
But even with all of these possible answers, I cannot think of a single reason why no other trainers would have Psyduck, Krabby, Scyther, Electabuzz, Magmar, Pinsir, Ditto or Dratini.
Gen 6 is the most underrated Pokemon generation. It gave us: >XY: the best initial pair of games >ORAS: the best remakes >Mega Evolution: the best battle mechanic >A lot of cool lore about Mega Evolution, the Draconids, etc
Just because we didn't get a "Z game" people perceive Gen 6 as "incomplete", but that's incorrect. My hypothesis is that Z didn't happen precisely because XY were fairly complete as is, especially compared to previous initial pairs. So instead, they finished all the lore with ORAS.