If there is one thing I'd like them to develop on, it's the use of non-battle goals and dynamics. Don't get me wrong, I want some good battles, but previous series have shown by pattern that the writers struggle to do many quality battles, thus things dwindle and fall out of balance after too long.
Usually Ash gets the lion's share of developed battles, one companion gets most of the gimmick focused ones (eg. Misty, Iris, the contest Pokegirls), while the remaining companion gets leftovers like the TR curb stomps or half-finished demonstrations if they're lucky (eg. Serena, Brock). Making things too revolved around battles means someone's gonna get screwed over or get the 'lame' bits.
While the SM cast feel unbalanced right now, they don't feel lacking in importance simply because they don't all battle. Many plots revolve around different agendas and abilities, which allows for more variation. It also means they aren't as reliant on plot armour as previous series, where if you didn't battle often it meant tons of action scenes where you relied on DEMs or were suddenly as experienced as the guys that trained the whole series (eg. the previously mentioned instance of Serena being able to match Ash despite minimal battle development).
Add to that SM doesn't feel as goal focused as the other series, which I do kinda like. Most of the characters have basic agendas to keep them proactive, but there's a lot more value on actual personality, compared to earlier series where if you didn't have some big ongoing competition you were in trouble of becoming the background companion, even if you actual character was okay.
Even Rotomdex sort of fills this criteria, since he mostly works as comic relief and exposition, but he has ongoing interest in finding new data and Pokemon to keep him motivated (especially since the region trips and Ultra Beast encounters allow him to actually progress a little in this).
