I think something that people forget a lot when they write about Rek is that he is nice, not good.
It's an important distinction. Rek is pleasant- he will smile and be friendly and even apologize for killing or trapping a fellow lifestealer.
But he's not morally good- not more pure than his fellow murder-game dwellers. He's not just some sweet innocent guy.
Rek is mischievous at best.
He likes the thrill. He's an Adrenaline chaser. He laughs when he escapes chases and loves finding traps set for him, just to see their faces when he escapes or avoids it all together.
This is not to say that the constant paranoia doesn't make him stressed, but that there's a level to it that he's always had, even before Lifesteal, and it's something he enjoys!
His primary goals lie elsewhere than gathering hearts and being "The Strongest", so yes, he appears less bloodthirsty and ergo less dangerous, less cruel than the other lifestealers. But Rek doesn't balk at death- he just understands that his place in this game is beyond the scrabble for the top position, to be the top dog. He also understands that he is not the prey either, scrambling for survival in a place where everybody wants 20 lives and so someone has to lose them. They can't all be the best, after all. This places him in a unique position compared to many of the others constantly struggling for power. Rek is looking for fun. Not hearts, not blood, not fights, not power or influence- just plain, good old fashioned fun.
Rek understands that lifesteal is a game. Part of that game is people's perceptions of you. Rek is nice, so people hesitate to target him beyond traps, something he can handle. Rek is pleasant, so easy to talk to- so easy to let things slip.
Above all else, Rek is perceptive. And it's not just out of fear.
He's Paranoid, He's Cautious, He's Stressed- But Rek isn't Scared.
Anyways my long winded rant on my favorite guy ever. There is something deeply wrong with him that I feel is so overlooked in comparison to other lifestealers who are much more open about what is wrong with them (bloodthirsty, power hungry, hunted for sport, etc). People often write him as the moral backbone, the scared, in over his head best friend, or otherwise paralyzed with fear and desperation. Really, I feel like he's having just as much fun with the danger as anyone else. He's just more vocal about the discomfort that comes with near-death experiences, as he doesn't have any weakness he needs to hide for his reputation or safety. He's just silly!!