A Supreme Being is the first creator of all reality. That is what a Supreme Being is. In mythology Hades arguably has more command of the setting as he gets all the souls of the dead, chooses their afterlives, is the older of the brothers and could if he wanted revoke the immortality of any of the Gods just he barely interacts as he focused on the underworld and enforcing mortality. Zeus could command most Gods and one of the most powerful but not all as Poseidon and Hera for example both had moments were they came in conflict with little fear. Supreme Being don't have to necessarily rule, Chaos is the Supreme Being as it's the original creator of all which is what it means.
The reason Hades was not worshiped was because he was feared even by the Gods in some versions but rarely interacted as he just didn't care wanting to merely focus on his job. Zeus and others appeared more but often because they were screwing with mortals thus more "involved" with mortals. Media tends to treat Zeus as the God archetype and Hades as the Satanic archetype but in myth that wasn't really the case just media pandering more to modern religious concepts/groups. As someone who's been obsessed with Greek mythology for many years I can say without hesitation Zeus may be the King of the God and arguably the most powerful (or at least one of them) but by no means a Supreme Being of the myths especially when clear others rival him (namely his older brothers), the world and life existed long before him.