Dark Forest depends on the presumption that interstellar travel is worth engaging in (ie it's possible to do faster than light), and that spectacularly devastating weapons are possible. So far we have no reason to believe that either of those assumptions is smart.
Faster than light travel isn't needed (and IIRC doesn't occur in the series the dark forest name comes from). Spectacularly devastating weapons are definitely possible - redirect an asteroid into an inhabited planet and you're likely to kill most of its inhabitants; redirect enough and you can kill almost everything. That's not even getting into things like antimatter, gamma rays, etc. The dark forest hypothesis doesn't need destruction of solar systems to be possible, just severe damage to civilisations.
> and IIRC doesn't occur in the series the dark forest name comes from
The Trisolarians developed FTL travel while they were on the way to Earth, IIRC.
I tried to look it up. I think they didn't ever get FTL, based on https://www.reddit.com/r/threebodyproblem/comments/1blvikg/c... and https://forums.spacebattles.com/threads/trisolaris-in-wh40k.....
Ah, yes, you are right. They managed to speed up their travel time to Earth greatly, but they did not reach or surpass the speed of light. I have to read the trilogy again.
They had the sophons which allowed them to convey information via quantum entanglement, i.e. instantly.
They - and the humans - developed close to light speed traveling which IIRC has the same underlying mechanics as that blackout-galaxy-safe-space thing which is the message that your civilization is not harmful.