The one thing missing from Legends, with its constant drip-drip-drip of XP, vaguely MMO feel, is a sense of connection with my pokémon. I remember having a fondness for my team in the GB(A) games that's just not here, for (I think) a few reasons.
Firstly, catching them is too easy. I've got easily half a dozen of each species chilling at my ranch; the number of times I've seen a new pokémon and just… caught it, with little to no fanfare or effort, makes each one feel more disposable than they did in older games.
But once they're on your team, they level up – and evolve – too fast. I barely had time to learn my starter Rowlett's moves before I got the evolution prompt. My Zubat evolved twice in one go.
This is probably a side effect of the easier catching mechanic, and the Pokédex checklist that asks you to evolve a certain number of each species; if that involved jumping through the classic games' hoops, that would be a mammoth task.
(And, once you've caught 22 Pikachus, it's a laborious process to release them all, so much that I've basically given up trying to curate the ranch. I don't know what happens if you run out of space.)
But the biggest missing feature, when it comes to building a bond with your pokémon, is probably that you can't name them.
This might be a deliberate choice rather than an oversight, tying in with the coldly scientific approach of Galaxy Team's Pokédex compilation, but when so many of Hisui's other residents are making a big deal out of how I've got a surprisingly strong connection with my pokémon (despite trapping them in balls), it's weird that the game doesn't let me, as a player, form that bond.