I really don't know what your deal is with Pikachu and why you're so against him but Pikachu and Ash are like two peas in a pod. You can't have Ash without Pikachu and vice versa. That said Pikachu is never going to be left behind and yes, this also means that Pikachu will be used for many key battles including gym battles. For Ash to not use Pikachu would be not showing the mutual bond that the two of them have (which, for many people, is already deemed a problem that there isn't enough of that bond with Pikachu in XY). That said Pikachu has been used in most gym battles to begin with so Ash not using his main Pokemon in anymore gym battles it wouldn't be Ash.
And please let's not forget Nimbasa, what I would say one of the worst gym battles, when Ash conciously wanted to leave Pikachu out of the gym battle. That was a mistake that should not be done again. If he isn't going to use Pikachu in a gym battle it should definitely not be in that manner and there should be very good reasoning for it as well.
Yes, Pikachu losing to certain Pokemon might be a pain but this isn't the games. You can't base a Pokemon's power based on level but on skill and far more.
But yeah, remember that this anime is more than just the gym battles. It's about the bonds and friendship Ash has with his Pokemon and while he, yes, keeps most of his regional Pokemon with professor oak when he goes to a new region getting rid of Pikachu, who was his first Pokemon, partner, and the Pokemon he has a much deeper connection to than any other trainer, it wouldn't be right. Arguably, as said before, we need to see more of that mutual bond that Pikachu and Ash have (BW did a pretty good job in this respect) than it current has in XY (which is one of it's weaker points).
Unfortunately, bonding or not, there's little point if they are going to have Pikachu's power be treated inconsistently to an extent that he looks bad. And it's not like they can't do that with any Pokémon without not bonding with them. After all, they did it with Ash's Kanto Starters, and it's pretty obvious he bonded with them. And they also grew stronger as well.
And I never said or even meant "level" as in gameplay, but the actual amount of experience the Pokémon has, which even in reality is somewhat of a factor in deciding the outcome of a battle or a match. Let's think of it this way: You pit a veteran, with a huge amount of strength and skill, against a rookie who is inexperienced and has no idea what he's doing, chances are very high that the veteran's going to win. That's what I'm meaning. And honestly, a Pokémon who is capable of effortlessly beating a freaking Legendary Pokémon (who are definitely reputed to being exceptionally strong Pokémon even in the Anime) most certainly can breeze through all except possibly the Elite 4 and Champion, that's what I'm getting at, and even ignoring the fact that Pikachu beat that Regice in Battle Frontier, having it lose to Gym Leaders, characters who, BTW, during Hoenn were treated as pansies for the most part and more often than not lose against rookies makes it look very bad.
And besides, they can have Pikachu forsake a match without it impacting his bond with Ash. Don't forget, he specifically refused to fight Misty back in Kanto, and that didn't impact their bond at all.
As he and Pikachu are at the heart of an anime franchise that tells more or less the same basic story with each new iteration with only a small connection to what came before, Satoshi's personality doesn't change that much and probably never will. This isn't to say that he can't develop and learn new things, or that his story can't be told in different ways (for example: Satoshi's journey in Diamond & Pearl was different from his journey in Advanced Generation...), but I have to imagine that whatever way he does develop is going to have to be limited by necessity. So to answer your question: no, Satoshi's personality following AG doesn't undergo any radical changes, but his story in DP certainly does.
This is one of the biggest reasons why Satoshi isn't fun to me in Best Wishes or XY. If you have a character who can't change that much because his story will need to continue into the next show and who's going to do the same thing each time, then he needs something new added to his journey to make it stand out. As much as I dislike Satoshi's story in Advanced Generation for how dull it often is compared to Haruka's it did get something out of contrasting Satoshi as a veteran against Haruka as a rookie, at least for a little while. And introducing Shinji as Satoshi's rival in Diamond & Pearl, and using him to actually challenge Satoshi's training style, made him more compelling in a way he never was before. BW and XY, meanwhile, do nothing new with Satoshi and Pikachu that hasn't already been done. Satoshi has never been a nuanced character, but he's been more bland in the last two shows than he's ever been and I think the lack of any clear variation to his journey is the reason why.
That's another thing my ideal version of Satoshi would have. A journey that has more to offer than simply a rerun of what's been done better in previous shows, something that's unique to that particular incarnation of the anime.
Yeah, and in regards to your comment/complaint about AG, it also doesn't help that Ash's Hoenn team for the most part tore through the Gym Leaders like tissue paper, even though their status as rookies compared to the Gym Leaders should have rendered that improbable, if not impossible, especially on the first try. I mean, I can understand Pikachu doing so, but not Treecko or Taillow. Just because Ash himself is experienced doesn't mean that all of his Hoenn team barring Pikachu should win against the gym leaders effortlessly and on the first try, especially when they are supposed to be challenges to be overcome. Having them beat the Gym Leaders like that makes the GLs no different than Team Rocket, especially when they were humiliated by a completely inexperienced, extremely weak, and, thanks to Ash's utter stupidity at that time, barely-even alive Caterpie despite their obviously having the advantage of being significantly more experienced and fresh in comparison (it even resulted in them, both by the fans and even in-universe, at least during Kanto, being designated as being extremely pathetic trainers).
Paul at least gave a challenge (though it still was somewhat poor when Paul had beaten Pikachu, despite the latter having just beaten a Regice. I was hoping that Pikachu at least lose against Paul's starter Pokémon, since at least that Pokémon was confirmed to actually have travelled around as many of the same regions as Pikachu (not counting Orange Islands or the Battle Frontier).), so that made DP somewhat forgivable, and even the gym leaders were slightly more challenging that time around, though I was hoping there would be more rematches from Ash than there were (two would suffice).
I want to see an Ash that would actually change as time went on as far as world views and ideals go. Then again I haven't seen the show since the Hoenn Battle Frontier arc so I'm unsure if Ash actually has changed a bit since then personality wise.
Well, depending if you consider Ash completely regressing to his Kanto self during BW for literally no reason at all and being turned into such an idiot that even Kanto Ash seemed far more intelligent than him, he did change as time went on.
