I honestly don’t know. People can suggest things on this site that might very well help, but you’re the one who knows the story. If you can’t write a logline that makes this film seem more of a “must watch” to people, then either you can say “well, it’s as good as it’s going to get for the story I have”, or you can change the story so it’s more interesting. Right now, I know nothing about your cyborg hunter, the cyborg, or the young woman… you’re totally ignoring strengths, flaws, and psychology. I’d think about that, and what would make a more interesting situation. I tried to suggest something like that with my logline, but I guess you didn’t like it. Maybe a cyborg hunter trainee? Or you can make it so it’s not even a cyborg hunter… like a bear hunter? Or! You can set up something like The Rock and team the cyborg hunter up with a science geek type. And then think about what you can do with the other two characters… hopefully there’s some relation so it makes for a coherent story.

I don’t think loglines typically assume familiarity with a particular character, nor do they generally include any names. You can easily just turn that “biggest mission yet” into the inciting incident. Also, you can add some urgency by taking out the uncertainty implied with the word “might”. Personally, I still think it’s a bit dry though. I want some sort of reason why I think the cyborg hunter might not succeed, which could be easily added with an adjective. My take on this:

After a traumatized cyborg hunter manages to escape from the cyborg homeworld after months of torture, he takes on one last mission, to go back and rescue a princess from the cyborgs before they turn her into one of them.