I just finished watching it last night.
Here's my take. Rust, left in misery after the seemingly random death of his daughter poured himself into trying to find light in the world. Sure, he had a shitty viewpoint of it all and that led to a lot of self-destructive type behavior, but in the end he realized he could prevent other fathers from losing their daughters.
Maybe it's because I have two daughters, but I saw both of the main characters from the perspective of their father/daughter situations. You had one that involuntarily lost his daughter and got lost along the way trying to recover from it. You had another that got lost in himself and willingly lost his daughter(s), but suffered some degree of the same pain. Both eventually came around to finding the asshole that kept raping and killing other father's daughters and found their own salvation in the end.
But, as someone else said, so many ways to interpret the outcomes in this show means that it's a thinking man's show, not some neat, tidy Murder She Wrote shit where you can figure out the entire ending two minutes in. The ending ultimately didn't rest on the bad guy being dead, it mattered on how the bad guy's death impacted the two main characters, IMHO anyway.