Lillie I can go with, along with Sophocles, but Mallow I don't think is a great example, with Lana only a cut above that. They struggle to make them stand out besides the usual 'jobber villain' formula, otherwise they lack much agency at all besides "look what a great cook/bubble blower she is". They're arguably the first companions not to have any defining character flaws, which cuts down any opportunity for a character arc or to hold stories just on individual personality. Even Lillie and Sophocles are kinda lacking in limelight at times, even if the core personality is fine enough. I think this is a storytelling approach the writers are still in 'baby steps' mode with, even if it's very welcoming to see them trying at all after relying on formula for so long. Some episodes actually feel like valid attempts at character studies (eg. Lillie's Poni Canyon episode).
Ironically Ash and Kiawe despite having goals, actually probably are the best for standing out as individuals and keeping fillers and spontaneous stories entertaining. It's emphasised by the fact they didn't even know about the league until very late into the show.
They also seem like the two characters the writers least have to 'kiddy glove' and are willing to accept they don't have to look good at everything. They have enough agency to redeem themselves from being a flawed 'loser' at times. There's a better sense of humility in SM from this, something we usually only see with Team Rocket. I feel like previous series (besides early OS in its cynicism) were a bit unwilling to crap on the protagonists too much, because they didn't always have a lot of character agency, maybe they worried not keeping them more on the 'winners' end of things superficially would lead them to look unremarkable, always having a straw loser like Team Rocket suck up all the stench of failure away from them. This still seems true with SM according to how bland or not a protagonist is. Ash doesn't need the plot making him look awesome this series however. Sure there is still some cases of plot armour, but he can go into nearly any story and make himself look like a badass, no matter how much things twist to turn him into a clown.
There is the downside that Ash's actual goal focus is a bit more half assed this series, but it's not downgraded enough to be utterly lacking in substance, especially since that helps with the other storylines, there's still enough to keep him look competent, just there's a greater focus on making him character driven this time.
On a side note, I also like how most of the characters that did get development this series had it tied into a specific motif, namely the 'fish out of water' premise. Characters that have a niche but have been sheltered or so used to being in their element for so long that they are hopeless outside of it and spend much of their time trying to accustom to things out of their comfort zone. It works for a series that has been trying most to break the formula.