I have to disagree. I think that Dean Ambrose at this moment is a prototypical antihero.
An antihero is a protagonist who uses unconventional and unheroic methods towards his end, such as Dirty Harry or Snake Plissken. They still pursue the goals of the hero, they are still the "good guy," but they do in a Machiavellian way. The most important factor is that despite their methods, they still have to be a protagonist.
Dean Ambrose is very much an antihero at the moment. He is a protagonist who uses less than traditionally heroic methods to accomplish his goal. He wasn't fighting Seth Rollins nor currently fighting Bray Wyatt towards any noble purpose. It's revenge, which is completely fine, but revenge is a major motivator of an antihero.
I see what you mean, but wouldn't that make him (as well as Dirty Harry) a tweener?
Steve Austin, in my view, was anti-hero in that he would eagerly kick Santa's a** (He actually did this December 22, 1997 on RAW), in front of children.
Anti-heroes would be the first people to kick a man when he's down or spit in the face of somebody with good intentions.
It seems Austin didn't like anybody, while Dean Ambrose only dislikes those who get in the way of his objectives.
I suppose its a fine line and maybe I'm reaching a bit, but I still see a difference.
If you recall
Batman:The Animated Series, Catwoman would be my distinction as anti-hero.
As Selina Kyle she was an animal rights activist, but as Catwoman, she wouldn't hesitate to tussle with Batman
Would Dean Ambrose stand alone and watch Dolph Ziggler get beat down without lifting a finger? Maybe.
Steve Austin was also an alcoholic, hit women and even attacked Jim Ross in the fall of '97.
I realize men attacking women is taboo in WWE these days, but Ambrose just doesn't have that evil streak in him.