dark energy really as strong as physicists state?

As near as we can tell, dark energy is evenly distributed throughout the Universe and can not be concentrated. Advanced aliens could only use dark energy to destroy us by destroying the entire Universe. They would do something easier such as redirect a few comets our way.

Dark energy is not energy, it is not negative energy, it is not anti-energy, it's what causes space to expand. We only call it dark energy because we don't know what it is and it's certainly not matter. Einstein had a better name for it, the cosmological constant usually signified by the greek letter Λ. He called it his greatest mistake, he never knew that he might've been right about it.

Aliens don't exist as per the evidence so far. Illegal aliens are a different story.