Prompto is a ranged support damage dealer and is a limited-time unit from FFXV collaboration. With a range of +3 (or +4 at the cost of some AGI) and an +AGI buff with an -AGI attack, he can widen the speed difference and be able to continuously attack from afar. He can also weaken an enemy through other ways, with 2 of his core ability having a chance to inflict either slow or Dark resist. If any of his status effect lands, he can deal high damage with Penetrate to finish off an enemy.
Unfortunately, his choice of status effects aren't that powerful, and while his sub job options are pretty good, it means that they are separated abilities. Main job as sub job provides a wide area grouping ability (Conductor) and 1 convenient ability that can reduce ATK/MAG/DEF/SPR of enemies in an area (Star Shell), but it deals no damage. Meanwhile, Sniper has Dispel Spread and Slow Shot, while Assassin has -DEF and more status effects through short range attacks.