True one recurring theme among prometheans is the idea of versatility, crawlers can fit in small spaces and climb most surfaces, but still carry heavy weapons (binary rifle), The knights depending on what equipment they have can be anything from snipers to demolitions, and those watchers are the perfect support troops, deflecting grenades, shielding troops, and resurrecting fallen allies. It would make sense that the soldiers would follow that theme, being able to use enemy equipment and if need be go from air assualt troops in phaetons to ground shock troops. That actually makes me think of their boarding action role in the human-forerunner war, maybe blast a hole through the human defenses with phaetons and then board with the soldiers piloting them.