Perhaps not need. Still, with Season Passes being a highlight of each season, then it feels odd to only have a few ghost shells hold this perk. Regardless of the "need," this won't stop players from playing many hours per play experience to get the XP, regardless, especially with the pass having many unique rewards that cannot be obtained anywhere else. So, maybe a ghost shell can be used when ONLY doing public events or ONLY when collecting resources, but for a majority of the time, the XP will be the most useful quality for the ghosts.