Is it really a bad thing to have one PC be more "important" plot wise than other PCs?
Maybe the story does start with the party protecting a prince or wizard or prostitute or whatever, and instead of having said character be an NPC, it can just be one player's character, with everyone else joining either for money, for friendship or for other personal goals.
Sure, the special NPC shouldn't get all the cool moments and favoritism, and if they die they just fucking die.
But it seems like it'd be an easy way for the GM to lessen the chances of the story diverging too much from prepared materials, while also making it easy for players to choose whether they prioritize story and roleplaying, or whether they'd rather focus on combat and gameplay stuff only, or whether they're only in the group to hang out with their irl friends.