Finished watching Indigo League and Orange Islands. Ash's journey so far highlights a lot of his early flaws and overconfidence, a stark difference from Sylvia.
Sylvia and Ash end up meeting in Johto, one way or another, thanks to the GS Ball (because it bothers me that that was never resolved, and I think tying it directly to the 4th movie would make sense since that was the reason it was cast aside anyway). Sylvia's early flaws are very different from Ash's.
Unlike Ash, Sylvia considers herself a loser, the type of person who struggles to win at any given opportunity, because she was often overshadowed by her two competitive, significant, and talented siblings. She would tell people she didn't want to see her Pokemon get hurt, and she genuinely didn't, so it wasn't a lie, but it was only the second reason why she didn't like battling.
In games, contests, battles, and any other competitive activity, Sylvia always lost to her siblings, who went all out because they enjoyed winning. It stopped being fun for her to play with them, because she just knew the outcome anyway. It takes a while for her to even build up any kind of confidence to start battling and taking her opponents seriously again, because this time it's not just her pride on the line, it's her Pokemon's pride, too, and they don't want to go on forever without battling.
First two regions of her travels, though, Sylvia is a very passive type of person. She's doing her best, slowly growing and building on her strengths, becoming braver every day. But at the end of the day, she's only 10-11 years old, and between the autism, her siblings' constant bickering, her lack of personal direction, and a history of some bullying in her school prior to journeying, she's just kinda lost the moment her siblings are taken out of the picture.
She's dependent on them. Getting basically adopted in Ecruteak City is what teaches her how to be a little bit more independent.
Jack and Lucy, on the other hand, have to learn many of the same lessons Ash did; overinflated egos, biting off more than they can chew, bickering amongst themselves, and add on to that the sibling rivalry, and the feeling of being held back by being forcefully tethered to one another until Lucy comes of age. Ultimately, this is what breaks the siblings apart for a time, then brings them back together.
Jack in particular struggles with the burdens of being the eldest, of having to protect his sisters and lead them when they also have minds of their own and want to derail his plans.
Lucy struggles with fighting for attention from her older brother, both in the sense that she wants him to focus on her, and that she wants others to stop focusing on him and overlooking her. She wants praise, for working hard, doing good, and ultimately, she doesn't want to be compared to Jack anymore.
At least, that's what I have so far. I'm still workshopping it a bit, since this also means people tended to just kinda ignore Sylvia. Middle kid syndrome at its finest, amirite? No but seriously, she wasn't really ignored so much as she just kinda... made herself invisible and people tried to respect that as much as they could. She also did her best to be as amicable as possible for others, and of the three siblings, she's the biggest people pleaser.
Now off to bed I go before I regret writing anything. Take that, anxiety demons.