You are misinterpreting what was written about "mastering a woman" as meaning that Wicca sees men as more important or ruling over women. Don't feel bad, in this case it is a common mistake.
First of all let me explain a bit about the "Old Laws of Wicca". They aren't actually old at all. They were written by Gerald Gardner during the 1950's when he was having a bit of a spat with his current High Priestess. Some of the laws were directed at her in particular. Gardner also purposely wrote these in the style of some older texts in an attempt to make them seem to be ancient, but trust me, they arent old at all. Wicca was started by Gerald Gardner in the 1940's.
Now, as to what the law you quoted actually means... We are not talking here about the man ruling over the woman. What this actually is interpreted as meaning could be summarized as saying; "As a man loveth a woman by becoming one with her, so shall they submit to the Wiccan gods and become one with them."
Remember, in Traditional Wicca all members of a coven are equals. However, within the circle the High Priestess' word is law. So power goes to the woman, not the man.