Sovereignty is much more than control. Sovereignty is about relationships and balance of power.
There's a lot of confusion about self-sovereign identity.
Many people hear sovereign and think "sovereign means the individual has complete control." Not really. As Scott David pointed out, "declaring yourself king of a deserted island isn't very useful."
Sovereignty is about relationships and boundaries. When we say a nation is sovereign, we mean that it can act as a peer to other sovereign states, not that it can do whatever it wants. Sovereignty defines a boundary, within which the sovereign has complete control and outside of which the sovereign relates to others within established rules and norms.
Self-sovereign identity (SSI) describes the same situation. A self-sovereign identity system (SIS) defines the things over which an entity (person or organization) has complete control along with the rules of engagement for its relations with other entities in the SIS system.
For example, an SIS might give entities complete control over what claims they share in response to queries about them. But sovereignty doesn't mean that a party relying on a claim has to accept it. The relying party's sovereignty allows it to determine what claims satisfy its demands and which don't.
But sovereignty means that all powers are reciprocal. Continuing the example, anyone can reject the claims others choose to present to them. The key to sovereignty is that all entities are peers. I have the same rights you do. The beauty of sovereignty isn't complete and total control, but rather balance of power that leads to negotiations about the nature of the relationships between various entities in the system.