I agree with you Rollo, when you say that none of the current players have dominated to the degree of Graf, Navratilova, Evert. I'm not familiar with the others you cited, but they sound like they qualify.
The first question was to set the standard for what really defines dominance.
My second question was to ask who of the current set had the potential to be that dominating, if any?
As to the definition of dominance, to me, unbeaten records / winning streaks is one way of looking at it. Another way is to look back on a particular era, and think of who were the defining players of that era-- the unbeatables, or the great rivalries that happened only between 2 players.
Ironically, I think that it is the very DEPTH of today's women's tennis that makes it difficult to pick a "dominant" player, even one in development. (Take that, Rios!) Men's tennis right now is the very epitome of no one truly ABLE to dominate the sport. Makes you appreciate Sampras and his run.