Ok, power tools cut through mountains like butter so that a single man can do stuff like this today.

https://www.youtube.com/watch?v=fyfxB_SqWtc

So it's possible. But who's paying for large temples to be cut out from mountain faces in today's day and age? We're achieving engineering feats that would make ancient people think that WE'RE the aliens. And there are people who think it's the other way around? We are where we are today because ancient people mastered the art of stonework back then. Forgetting or ignoring that and attributing it to aliens is disrespectful to our history.