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.
You're wrong about the theory side of things[1, 2], by the way. The discussion around adiabatic quantum computing is weirdly politicized. It's true that D-Wave's computer isn't a universal quantum annealer; but in theory such a thing is equivalent to a gate-model computer.
[1] https://arxiv.org/pdf/1611.04471.pdf
[2] https://iopscience.iop.org/article/10.1088/0256-307X/35/11/1...