Gunn says himself Drax is the strongest member, see my other post.
Can't agree he came closer than most to achieving his goal, think many other villains were much closer.
I certainly didn't mind Ultron's plan, or his personality, so I wouldn't say I wanted a different villain. I just wanted a good one. A good villain doesn't get his ass kicked regularly, he comes across as a threat to the hero/heroes throughout. Ultron never came across as a threat throughout, despite his original plan being getting rid of the Avengers. He was just poor in this aspect. I know the heroes are going to win most of the time. But a good villain has me questioning if or how the heroes will beat him/her.
I had that with Ronan, I had it with Kilgrave, and I had with many more villains in other movies. With Ultron there was none of that, no tension at all to the movie and how he was going to get beaten and his plan foiled. He isn't the only Marvel villain to do this, but I certainly expected more from Ultron. In the comics he is constantly a threat, and a big one. In the movie he wasn't a threat at all, and that was the case literally from his creation onwards. It was simply poorly done.