Vazquez is a special defensive talent. No, several teams do not have catchers that can play defense like Vazquez can, though the Nationals seem to have one, at least through the minor leagues. There are no 'clones', plural. Just one clone.
Who knows why the Nationals were willing to part with Leon over Ramos or Lobaton. Maybe they don't value catcher defense as much as the Sox do. Maybe they feel that with their great pitching staff, they don't need the pitch framing as much as they need the offense from that position. Maybe they felt that Ramos and Lobaton are both better overall catchers because Leon's offense is so weak.
Why will there be a negative impact on our defense from losing Vazquez? For one, there will be a learning curve for Leon in getting to know our pitchers. For two, Leon will not be catching as many games as a healthy Vazquez would have been. For three, I don't know how proven Leon is at the major league level.
All that said, I have also said that I feel less concerned about the loss of Vazquez since Leon was added.