No, it is not pointless. Вы MAY be a formal way of saying singular you, but it is also the only way of saying plural you. In this exercise вы is being used in plural, so вы is NOT replacing ты here. There is no way of using ты in this sentence.
Ты - You (singular, informal)
Вы - You (singular, formal)
Вы - You (plural, informal)
Вы - You (plural, formal)
How plurality is expressed depends on the noun's case. This might help get your started: http://www.russianlessons.net/lessons/lesson11_main.php
Not wrong, but rather strange in English to use the definite article here, I'd say.
It's rather strange to be stating something obvious like: "You are women" in the first place, but even stranger to say: "You are the women."
We can't really know, without further context, but as none is given, better to leave it out, in my opinion - it certainly reads more naturally.
"женщины" is plural - women. So the translation can't possibly be singular (woman). Further, even though the phrase may sound a little odd or unusual, because we don't often need to tell women what they are, there's nothing grammatically wrong with it at all. Telling a group of people: "You are women" is not really any stranger than telling one person: "You are a woman."