But their entire plan...
And what do you think their plan was?
...and adding the Borg Queen were terrible.
Why shouldn't the Borg have an embodiment of the Collective mind?
After all, if you have billions of drones connected together, why shouldn't they function as one mind? Your brain cells do it easily enough. And why shouldn't the Queen be an individual, emoting all over the place? Your brain cells don't have any individuality and can't emote, but when they all act as one, they form your mind, don't they? A mind with a sense of individuality and emotions. So why should it be so implausible that the Borg do exactly the same thing?