The difference being that all those returning characters you mentioned appeared in at least 2 consecutive episodes, meaning we have more opportunities to see new and old dynamics.So with the knowledge that Iris'll be returning pretty soon some people think'll it be treated how like the return to Alola was treated; With Goh taking up focus to get to know the older cast. Personally, while I DO wish his goal could be handled differently, i'm indifferent to him. So I just gotta ask; Hasn't the return of a previous character always been treated in such a way? With the new character getting to know the old?
When Misty returned in Hoenn didn't she spend more time with Max, bonding over being younger siblings? He even started pulling on Brock's ear like she use to. With May returned in Sinnoh Dawn recognized her as the Princess of Hoenn and the two became best friends pretty fast. When it was Dawn's turn to come back she and Iris bonded quick and liked to tease Ash. If Iris had come back in Kalos I bet she and Serena would have gotten along, and Serena with the Alolan cast
I feel like this is how its always been After all, we had already seen their dynamic with Ash through a whole region(in Misty and May's cases, multiple), so doesn't it make sense to see how the old character's bounce off the new ones?