As with everything else, it's possible to do character development badly, but I don't think it's as bad as you make it sound. Compare Bianca and Cheren with Hugh.
Bianca is going on a Pokemon journey to find her independence as a person. She and Elesa confront her father (who may merely be overprotective or outright emotionally abusive; both interpretations are possible, and you can form your own opinion) but through her interactions with you and Cheren she comes to terms with the fact that the path you seem to be pursuing isn't hers, ending up assisting the professor with research since that's what she finds rewarding.
Cheren's goal is to become the Champion. His use of held items rather than Potions conveys his strategic nature and lends a sense that he has the makings of a strong trainer in him, but when Alder asks what he plans to do after he's on top of the world he has no response. Being the League Champion in Unova isn't like climbing Everest, where "because it's there" is a valid reason to do it; it's a role with a significant amount of influence, and Cheren has no idea what he'd do with that even if he did get it. In the end, N explicitly chooses you as his counterpart over Cheren, who bows out with grace (but still succeeds at fighting his way through the Elite Four, as if just to prove to himself that he was at least in with a shot) and becomes a Gym Leader, using his expertise and wisdom to assist his fellow Trainers.
Hugh is a kid who wants to get his sister's Purrloin back. He shouts a lot at people wearing Team Plasma uniforms, ignoring any nuance in the scenario (like the former Team Plasma members wearing their old uniforms as a symbol of contrition and loyalty to N); he cares about Pokemon, and thinks that things like stealing them and making them sad is bad in the abstract, but he only actually cares about his sister's Purrloin. Eventually he gets back the Purrloin, and he crashes to a halt as a character. The battle in Victory Road is a formality - previous Pokemon games have a rival fight in the run-up to the Pokemon League, so here's Hugh again.
First two paragraphs are so easy to write from a character development PoV. It's so overrated it's not even funny to me. It's not like I don't get what said characters are supposed to experiencie in theoir journeys, i've a grade in spanish philology, I know what I'm referring to when I say both character development and narrative.
Bianca is a
cliché that ends nowhere, so her motivations are not only irrelevant but also incongruent from a narrative perspective, because they don't contribute no anything the character comes with later. Also, she's another example of character that, somehow, redeem herself and her vision of the world through contact with her friends, but she does it in the worst of ways. Imagine if she had stayed with her father from the very beggining, assisting professor Juniper, which is what she ends doing. There you have it, no familiar drama. It has no substance.
Cheren's realization is taken from a bad Shounen. "What are you going to do when you get there?" Hmm I don't know man, serve as the formal Champion and live out of it? Because the Pokémon Champion GAINS money, the Pokémon League, if you want to put things that deep and literally, is an official institution that every region has, an official exam you've to pass in order to become the next formal champion and, of course, gain money and prestige with it. I can buy that being the champion wasn't Cheren's true aspiration, but it isn't like "oh, i've climbed the Everest, what should I do now...". It's more like "oh, I've won the Pokémon League, now I can do wathever I want". Another example of
I've done everything well but now I don't know what path should I choose, my achievements are fulfilled and yet, my soul feels empty character.
Ok. Let's abstract from the games. Do you think you can just approach a student and ask him/her "what are you going to do when you finish this", only for him/her to inmediatly experience an epiphany and realize that, in the end, his/her life has no sense? That works in shounens, videogames and literature, not so well in real life, which is what a real character development should look like, even if not as epic. Because Cheren answering "I'll gain money and then I'll see what I do next, but first i'll concentrate in winning it" to Alder, even if deeper, doesn't sound as dramatic.
Hugh has none of that. Hugh doesn't care about Pokémon more than you would care about them. Hugh has only 1 thing in mind, a violent, almost excessive attitude towards Team Plasma members because they've harmed his sister. I'm so tired of characters that end forgiving the bad guys because forgiving, somehow again, is a great thing. Hugh pursuit this same goal from the beginning to the end, doesn't change because he doesn't have reasons to, recovers his sisters Liepard and, if I remember correctly, doesn't even forgive the bad guys. That is a character I can relate to.
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