I'm thinking Jesus made a distinction in Mt 16:19 between Peter (petros, small rock) and this rock (petra, mass of rock) because this rock is Jesus himself (Mt 21:42;
Eph 2:20-21; Ac 4:11; Ro 9:32; 1Pe 2:6)
on whom the church is built.
It is the body of Christ, and no one else on earth, which
has the keys to the kingdom of heaven; i.e., the gospel, binding and loosing, in the preaching of the gospel, what has been bound in heaven and what has been loosed in heaven (Jn 3:18, 36).
Looks like I am in pretty good company with this understanding. . .some of the church fathers.