I consider this a disproof of the "dark forest" hypothesis. That doesn't affect the Three Body Problem as a work of science fiction at all; science fiction gets to make a few assumptions and then ride from there. But if it were advantageous to pre-emptively nuke anything that looks like a threat Earth should have been toasted hundreds of millions of years ago.

(And no, the dinosaur asteroid was not it. If an alien species is going to destroy Earth, they will destroy it, not slightly inconvenience the biosphere.)

It did take using the sun as an amplification source.