Plus as minor as it was I enjoyed having conflict between Pokegirls for once and see some clashing personalities. Misty and May were amicable but nothing memorable, Dawn and May got along famously but they have shared experiences as coordinators, Iris and Dawn got along well and Misty connected with Lana and was friendly with Lillie and Mallow. Chloe being a punctual worry wart, kind of a stick in the mud vs Dawn being more adventurous and more willing to stop and enjoy the scenery I just find it altogether more engaging than in BW where she was just there for 6/8 episodes she was around
I dont think many people mind the Dawn Koharu interactions. Its the lack of other stuff that bothers people, me included.
See when misty came back the first time, we got the entire togetic arc, that was heavily focused on her.
When May came back, she essecntially contributed to Dawn's growth, while also showing how far she has come, and showing that there has been sone growth in her character.
When Dawn came back in BW with a Quilava, you got to see that there has been some growth in her journey as well.
Misty and Brock in SM came back with Megas. You get the point.
There is in no way a problem when the returning companion comes back to aide in the growth of the current companion. The problem is the returning character doesnt have to be treated like they havent done much since the last time we saw them. These things arent mutually exclusive. We can get dawn contributing to chloe's arc while she has meaningful interactions with Ash, and also showcasing the growth of her character.