Well, if we look at how Thanos was defeated last time:
Eeee-yup. That oughta do it.
Let me explain this a bit: A direct hit under the jaw with enough force is capable of immediately knocking out a human being. A human fist is fairly light-weight (20 ounces), yet the velocity of the punch from physically-fit person can increase the weight of the impact a thousandfold. Extend 20 ounces to 42.3
pounds (the weight of Mjolnir), and the massive amount of physical fitness Thor possesses, not only would that kill an average human being, but for someone as strong as Thanos it would take that much force to knock him into the air; in a nearly-unconscious daze. The final blow from Iron Man's unibeam, which slammed him into the dense pavement at a vast speed, is what finally knocked him out cold.
He's not really a chump, but the powerhouses on the Avengers' team stand an equal match against him when given the right opportunity. I would keep an open mind for how he performs in the season finale. ^_^
.....Am I the only who thought of this, other than the writers? XD