So, the aliens will be in trouble and will need humanity's help 3000 years after their 1st Arrival on earth. So, why did the aliens arrive on Earth so much in advance?
Question Context 1: Jesus Christ was born 2000 years ago. Some believe that literally, some metaphorically and some don't believe that at all. Humanity is divided on that.
The aliens and Louise, who understands and thinks in their language, will be the Jesus Christ of people 3000 years in the future. i.e. disputed figures. So the aliens will again have to bring everybody on board.
The video evidence of now will be equivalent to the written evidence (Bible) for people 3000 years in the future. So why not arrive in another Louise's (different person) timeline i.e. say 50 years in advance.
Question Context 2: Louise will die in about 50 years. For people to believe in what happened, she will need to pass on her gift to future generations. Hence she writes a book in her future.
A power to see your entire timeline. I can think of a thousand ways that can be used by evil forces to destroy each other. Remember, 3000 years is a long long time.
The Chinese President is a decent, honorable fellow and he takes initiative to bring all the leaders together. But isn't there a slight possibility that the most powerful nation in the world might somehow elect an evil megalomaniac that can use this gift to wipe out our entire existence before even the next century. So, again, why arrive so much in advance and not in another Louise's(different person) timeline?