There are currently two types of people populating the planet: Those who believe the story for Pokemon Sword and Shield is seriously lacking compared to Sun and Moon, and those who refuse to believe anyone plays a Pokemon game for its story.
Some Pokemon fans do indeed enjoy the games' stories—Yours Truly included. I don't expect Pokemon's narrative to engage me with the same depth as a Final Fantasy game, but the Pokemon series is almost always willing to tell an interesting story to anyone who'll listen. Pokemon takes place in a universe where sentient animals are at the beck and call of the human trainers who "own" them; if you don't think the games' stories don't suggest "Hey, isn't that kind of weird?" once in a while, you're mistaken.
As for Sword and Shield's story, it's not a non-entity as some fans claim. Character development is very much present—you just need to know where to look for it. OK, here's a hint: You'll find most of it in the end game. Helping Hop grow as a trainer is just half of the experience. The other half is in the "rare" trading cards the Gym leaders give you after you help them subdue the Galar region's unruly Dynamax'd Pokemon. When you put these cards together, you get a good picture of how the leaders connect to each other. You can also suss out the sometimes-painful journeys they've been through. It's a nice, subtle way of telling part of Sword and Shield's story, a bit like how the murals in Fire Emblem: Three Houses tell their own side-tale.
Galar is sport-crazy, so it makes sense that Gym leaders all have their own set of trading cards. Each one has a photo on the front, and some biographical information on the back. Some of this information is pretty personal; I don't know who wrote it, or why the leaders are OK with it being in public circulation. Either way, it's PokeFans' gain. This is the stuff I enjoy most in RPGs.
To see a full set of the cards and their text, visit Serebii.
Nessa is a model as well as the Water-type Gym leader - Fan-favorite Nessa isn't just a Gym leader: She models as well. Apparently, some people believe they're different people because "she shows a completely different attitude in each role." She's always calm on the runway, but if she's in a bad mood while stationed in her Gym, she'll skin you like an eel.
Piers was a complete dork when he started out as a trainer - Piers, the angst-ridden Dark-type Gym leader and figurehead of Spikemuth, is easily recognized by his eyeshadow, long black-and-white dreads, and his punk get-up. Even his signature contains a skull. That's 2 edgy 4 me, so let's look at his rare card. Notice the lack of eyeshadow, the bog-standard trainer's uniform, and Pier's inability to even look at the right camera. It's clearly the card Piers made for himself before he started his Pokemon journey. (You make one yourself, as does Hop.) I support this doofus in his endeavor to put Spikemuth's Gym on the map even though it lacks a Dynamax spot.
Melony and Gordie are an estranged mother and son - If you pick up Pokemon Sword, you'll face off against Gordie's Rock-type Gym. If you pick up Pokemon Shield, you'll face off against Melony's Ice-type Gym. The trainers' trading cards reveal the two are related, but they don't get along. (Gordie's gas-pain grimace should be an obvious clue.) Melony wanted Gordie to take over her Ice-type Gym, while Gordie wanted to go his own way. Melony's rare card suggests she's still the premiere member of her son's fan club, however.
Kabu struggled for a very long time to become a trainer of note - When I got Kabu's rare card, I wondered why he handed me a copy of his common card. Then I looked closer and noticed the cards are indeed almost identical, except the rare card shows a Kabu with darker hair and fewer wrinkles. Both cards mention Kabu suffered a long losing streak before he regained faith in himself after an epic battle against the Galar champion, Leon. Interesting sidenote: Kabu is from Ruby and Sapphire's Hoenn region.
Allister is just a scared little boy—and he might be undead - Time to get creepy. What, you're surprised? This is the same series that gave us Lavender Town and a Pokemon that wears the skull of its dead mother. Plus, one out of every four Ghost-type Pokemon sustains itself on children's souls or something equally disturbing.
Allister, the Shield-exclusive leader of Galar's Ghost-type Gym, always keeps his face covered with a mask. However, his rare card depicts him clutching his mask, seemingly on the verge of tears. The rare card's text admits Allister is very much "a normal boy" with fears and insecurities that he typically keeps bottled up. Meanwhile, Allister's common card claims he gained the ability to communicate with ghosts after an "accident" he suffered as a four-year-old.
Let's tally the score. We have a sad little boy who gained an affinity for Ghost-type Pokemon after going through a near-death experience. He's the youngest Gym leader in Galar; he doesn't seem to have parents. Most interestingly, close inspection of Allister's eyes reveal they have a strange glow where other characters have normal pupils.
My guess? Allister can commune with Ghost-type Pokemon because the aforementioned accident left him as something of a half-ghost. He's perpetually sad and scared because the same accident killed his parents.
Too harsh? Nah. The Pokemon series kills parents like Hydro Pump kills Rock-types. Pokemon doesn't care.
Bede's not a bad kid, he just needs direction - You actually have two rivals in Sword and Shield: the friendly Hop and the sullen, sarcastic Bede. Much of Bede's major malfunction seems to come from the fact he's an orphan and a little aimless. Despite his cold attitude, he's easily led around. Bede is eventually dragged off by the Fairy-type Gym leader Opal to be trained up as her successor. Though he moans about his fate to whomever will listen, the rare trading card he shares with Opal suggests he mellows out under her strict tutelage. Apparently, Fairy-type Gyms are the Pokemon universe's answer to military school.
Raihan, the Dragon-type Gym leader, has the best signature imaginable - It is literally a dragon, you guys.