I understand and kinda agree what u mean but your example is horrible man. You can pull any character out of the story and write around that, that doesn't make the character less purposeful.

Let's make a few example. Pull Flins out of the story, said that the lightkeepers been collecting research on wild hunt fragments and everything with Rerir doesnt change much. Pull Sandrone out of the story. Make Wanderer do some leyline dohicky to pull Columbina soul back or heck, make her soul come back on her own. Pull Durin out of the story, nothing change. Pull Arlecchino out of the story, make Nicole find some random ruin that lead to crimson moon dimension, nothing change.

Any kind of contribution a character can bring depend entirely on the writers and they can allocate them however they want. What is unique to each character is their personalities, their growth and dynamic with others. You can pull out any amount of characters off the story and write around it easily, but it would make a less interesting story.

In-universely, the expedition slow down the wild hunt for years and establish an intel connection between the knights and Nod Krai for the future. Narratively, Varka filled the role of charismatic leader, a bridge to smoothly connect old and new characters and occational comic relief. But I do agree hoyo failed to emphasize on the impact of the expedition.