I personally think the biggest advantage of weight lifting is when you look at the movement patterns of heavy lifting. Squatting and deadlifting for example are essential for your body to be able to do just as part of functioning properly day to day, whether or not you use weights. I think heavy lifting is beneficial to a point, but mostly for people who aren't already good athletes and don't have a solid base of strength. I also wrestle though, and think it's more important for that than for boxing as long as the you can do the form unweighted.

I find it interesting that Rousey says that, she often appears to be much stronger and more athletic in general than her opponents. Greatly superior technically as well of course.