I think it's wrong to say that just because the captain, as a character, is listed first in the credits it automatically means the show is about the captain, and the rest of the characters are only sidekicks. True, the writers of Voyager sometimes made it feel like that, but that was their mistake. The Trek shows are not about captains and their underlings, they are about a group of people. And groups of people change, in real life and in fiction. It alters the dynamics of a group when someone leaves, but that doesn't mean the group has to be less then they were. DS9 showed us that with the Relaunch. Sure, half the crew was gone, but after a while the remaining crew and the new members formed a whole new, interesting dynamic.
Everyone's important. But to think that a group can no longer survive without a certain person, is (in my honoust opinion) wrong. It will be different, certainly. But the group, the family, can go own.