Adequacy is the state of being sufficient for the purpose concerned. The meaning doesn't suggest abundance or excellence, or even more than what is absolutely necessary. Adequacy is simply the state of sufficiency.
There is a current of equality running through the noun adequacy. The Latin word from which it is derived is adaequāre, "to make something equal to something else." The English word made its appearance in the early 1800s as a derivative of the adjective adequate. Adequacy means being equal to the requirements of the situation — no more, no less. Theater critic Walter Kerr once wrote this scathing review of an actor: "He has delusions of adequacy."