yes I can agree to that. I mean i figured she was building a White Zetsu army for something. But Aliens just seems too far fetched for me. Why not another continent? Last I checked Aren't the 5 great nations on the same contient? Aliens could be simply Foreigner from another continent. Maybe that's where Kaguya is from.
To be more exact, I do not believe that Part 3 is very possible.
I also am not a fan of 'people from another world".
I see the things like this.
For the entire series we see people who would naturally look normal, that could perform supernatural things.
Then at the end of the series comes this family said by Kishi to be from another world, and this Kaguya whom naturally has horns and wants to build an army when she already could defeat the entire Earth alone.
She does not speak too much, and is also clumsy. She was said to be very strong, but doesn't show too much of the power.
She looked more like a teaser for the real thing instead like a serious enemy.
Then Kishi says Otsutsuki are from another world, and also Hagaromo says he could be seen as an alien. He also says Kaguys came from a faraway place.
Those things seem not to fit very well into the plot.