I've always had a problem with the equivalence concept. To begin with, energy is an abstract reality. It keeps changing form, always flowing to counter differences. Mass does the opposite, it concentrates, attracts other masses. An object is motion made up of a specific set of matter, is said to possess, some more mass, but this looks like an incomplete story. If I throw a piece of silver does the extra mass take the form of nuclear energy, some more particles of silver or something else? Everything that looks stupid is because it is done incompletely, as is the case here.