I've explained this in other places, but Writing 101 is to not replace your main characters with an unestablished character, and do NOT establish said characters at the expense of your main characters.
Take, for instance, the Lord of the Rings. That series has several secondary characters, some of which get even more time than Frodo and Sam. But the series took the time to flesh them out before that point. You know Gandalf, Pippin, and Merry. You understand Aragon, Legolas, and Gimli. They don't just drop a random dude on you, and push the characters you've known into the background.
That is Wuk Lamat in a nutshell. To use a different comparison, let's use the Harry Potter series. It seems like a fitting comparison. 7 books, and DT is 7.0. Let's say you read 6 books, all about Harry's adventures, and struggles to defeat Voldemort. Book 7, is suddenly about a character mentioned in a single chapter at the end of book six. And in book 7, Harry has almost no lines, has almost no interaction with the plot, and only exists to make this new character look good. Oh, and of course, the new character gets the killing blow on Voldemort, because of course they do.
That is Dawntrail, right there. A character with no development, no establishment, suddenly taking center stage at the expense of every established character around her. Even if they weren't one of the worst characters in the game, that alone is a cardinal sin of writing.