When an offshore patrol vessel becomes a corvette

Is the Braunschweig class a corvette simply because it carries a larger main gun than the River class?

Firepower is the practical dividing line, but fitting a larger gun to a River could dangerously overstate what the patrol vessel can do.

A River-class hull could physically receive a larger gun, but that does not make the resulting mission sensible. Added armament can tempt political leaders to send a lightly protected patrol ship into tasks better assigned to a frigate; the Braunschweig is a corvette because its combat fit supports that role.