The Closest DnD (5E) Class To A Helldiver Is A Warlock, Change My Mind

Warlocks have patrons - Helldivers have Lady Liberty/Super Earth/Managed Democracy

Warlocks can have familiars - Helldivers can have Guard Dogs

If Warlocks break their pact they'll probably die (or worse) - If Helldivers commit treason (i.e. leave the mission zone) they will die

Warlocks have strong spells but limited spell slots that take a long time to recharge - Helldivers have strong stratagems, but they can take a long time to recharge

Warlocks can have very different playstyles - Helldivers can have very different playstyles