Yeah, that question you asked is EXACTLY one of my complaints about him being stuck in a school environment, and is also one of the reasons I'm deeply outraged over the mishandling of the Kalos league, even if I ultimately think it was a better result than the Unova league due to Ash at least getting better than Sinnoh rather than simply returning to Sinnoh's level. Seriously, he's been proven to not even NEED school to be a good trainer as far back as The School of Hard Knocks all the way back in the Indigo League two decades ago where he managed to beat that top student Giselle with his Pikachu (and to make things MORE impressive, he used his Pikachu against a Cubone, and managed to beat it through indirect means by knocking it out via having its bonemerang hit it instead). And honestly, keeping him at 10 or not (which is stupid anyways...), if they didn't have him go to school for the past two decades until Sun and Moon, they really shouldn't have bothered doing it now (the best opportunity to do that would have been, say, the Orange Islands saga, which is technically the second season of the anime). Not only that, but it massively wasted Ash's abilities and development ultimately (they would have done a far better job development wise if he was dispatched by the Pok?mon League commission to help set UP the Pok?mon League due to his role in quelling the whole Team Flare incident, regardless of whether he won or got runner up), and all because of both the games getting RID of gym battles and the anime trying to compete with Yokai Watch apparently.
As far as the Alola league, true, it's probably going to be a lose-lose situation in this case, but there's not much better options, and personally, I think him even winning the league at all would work at this point, no matter how its done. Do I necessarily like the option of him winning cheaply and it feeling unearned? Absolutely not! But after 20 years of pretty much being denied even ONE win due to stupid reasons (or at least, one win from the actual games, since the writers apparently don't count the Orange League for some stupid reason like it being an anime-only region), I'm even willing to take a cheap and undeserved win if it at least ensures Ash wins for once. Call it desperation after being denied any chance of actually WATCHING Ash succeed in his goal, or do much more than simply improve (and even that and any other development he might have had in the series pretty much getting undone by the next thanks to the pointless level resets. The only time such a level reset was even REMOTELY justified was in AG due to Pikachu having recovered from a cold at the time, and even THERE, at least Pikachu beat Roxanne easily.).
As far as the returns for Misty and Brock that might occur with Pok?mon Let's Go!, personally, nostalgia doesn't even FACTOR into why I want the characters, or at least Misty, to come back. Actually, in Misty's case, it's mostly so the writers can redeem themselves for their otherwise horrid treatment of her since GCYL, like forcing her into the Pok?mon Gym thanks to her sisters, and constantly forcing her back there instead of having her, I don't know, continuing her goal and dream of Water Pok?mon Master, the implications caused by how grossly mishandled the Hoenn Gym Leaders (and to a certain extent the Sinnoh and Unova Gym Leaders) were that she's if anything going to atrophy from continuing to be beaten up by rookie trainers or at least rookie teams like some sort of punching bag (seriously, I fail to see how that's even WORTH her "not simply being Ash's girlfriend" as even some fans claim about her. At least being "Ash's girlfriend" would at least have more of a chance of her, you know, actually advancing in her goal by travelling and getting stronger rather than being constantly beaten up by people she should be able to handle very easily, thus making her look like a terrible trainer in the process akin to Jessie James and Meowth.), among other things like constantly denying her a reappearance in the flesh in DP (despite Mayumi Iizuka strongly implying she'd reappear in that series in her blog), not to mention BW (thanks to their stupidity in not even allowing Misty, Brock, heck, most of the cast at that point who wasn't named Dawn to reappear via the whole Pok?mon World Conference thing, despite it being a silver platter opportunity to have them return, by outright skipping the whole thing despite it being something from the games), and Kalos (which barely even included ANY continuity at all), and to add insult to injury, neither she nor Brock were even allowed to appear barring a brief cameo in the credits of Movie 20, and that was DESPITE it essentially being The Path to Power of Pok?mon movies (ie, a loose retelling of Ash's first saga). The Kanto Reunion arc came pretty close to redeeming themselves, including revealing that, thanks largely to her Mega Gyarados and her strategy involving it, she was nigh-invincible (and in fact, Ash was the first person to EVER bypass her strategy, let alone beat her), having her truly redeem the Gym Leaders' honor after AG pretty much stole it from them (Brock too, BTW). Even there, since Brock, who was repeatedly stressed to be a former Gym Leader in the episode, managed to handle his opponents far better than she did, she's still got a ways to go before the writers truly redeem themselves, like actually being allowed to pursue her goal instead of being holed up in the gym thanks to her sisters. Believe me, I've got a LOT of personal reasons for wanting any opportunity to have Misty and Brock (ESPECIALLY Misty) return to the show. I'm not even asking at this point that they return permanently, just have Misty, if she leaves, actually leave to pursue her goal and dream of Water Pok?mon Master, like how most of the cast after her managed to do so. I hated how they handled GCYL and her departure largely because of how they forced her to put her goal on the sideburner, not even having the opportunity to choose freely to change her goal. At least Serena, Brock, and to a certain extent Gary actually CHANGED their goals of their own free will with little to no involvement from others in their decision. Heck, even Clemont at least returned to the gym willingly, which is more than what happened to Misty, where she was outright forced to return to the gym by circumstances beyond her control. And while Brock definitely regained my respect for him in the Kanto Reunion arc, especially after the writers quite frankly ruined him back in Johto, and especially in AG onward to DP when they turned him into a Glenn Quagmire clone, and I do genuinely wish for a return from him as well, I also won't mind if he doesn't return too much (though I would be disappointed a bit in his not returning this time around).
In fact, to be honest, the prospect of Misty not only returning once again, but also resuming her dream of Water Pok?mon Master once she leaves instead of being forced back into the gym again before the end of the show and Ash potentially winning the league this time around (especially after what happened in Kalos) are the ONLY reasons why I'm even willing to put up with the Sun and Moon series (and believe me, what I could gather of it, it's even WORSE than both AG and BW combined. At least those shows still had Ash focusing on his goal.).
