This scene that you have identified presents Lear in a rather pathetic light as he wanders around seeking shelter during the storm on the moor. We get the feeling, as we hear his violent and somewhat unhinged denunciations of his two daughters, that he is beginning to lose his mind. Note the way in which he says "My wits begin to turn." Clearly, the way in which Lear is expelled from the households of his two daughters and treated terribly by them would suggest that Lear is indeed, as he calls himself, a man "more sinned against than sinning."
However, at the same time, let us remember that it was he himself that gave Regan and Goneril the power that they later used against him. It was he that intentionally exiled the one daughter that did truly love him and put himself in the power of the other two. Therefore, although he is definitely "sinned against" in the way in which his daughters treat him, at the same time, perhaps we need to be slightly wary of trusting Lear's words. It was his "sin" that created this situation in the first place, and if he had been a wiser king he would never have left himself open to the abuse of his daughters.