The winning condition shouldn't exist within the open-world PvP sandbox but outside of it. The matches should only be the means through which you get the necessary equipment and resources to progress through the real game.
And what would this "real game" be? Well, if I were to direct a new iteration of The Last Of Us Online, the "real game" would be garnering enough resources during incursions into any given American city sandbox (the extraction shooter part of the game) to sustain your group of survivors over the duration of a season of the game, while meeting as many arbitrary conditions along the way to unlock the most stuff possible from the battle pass, all of which would have a theme exclusive to that particular faction of survivors you'd be guiding through the post-apocalypse (maybe one season and its battle pass unlock conditions would be themed around a group of gun dealers, so you'd be required to focus on the extraction of guns and ammunitions during the runs).