An adiabatic quantum computer is equivalent to the gate model. D-Wave do not have an adiabatic quantum computer, so there is indeed no reason, even theoretical,

An adiabatic quantum computer is equivalent to the gate model. D-Wave do not have an adiabatic quantum computer, so there is indeed no reason, even theoretical, to believe their hardware provides computational advantage. The word "quantum annealer" is just a confusing term used differently by everyone, occasionally meaning "adiabatic quantum computer" and occasionally meaning what D-Wave have.