Does the redemption guy just gloss over the rest of his companions killings though? It works great if everyone is on the same page. Otherwise its usually one hypocritical pacifist traveling with, and ignoring the actions of, a group of violent killers (by modern standards) or constant bickering over the use of force and dealing with prisoners the rest of the party doesn't want.
Sure, there are some tables where the body count is low, and they take an actual look at the PTSD that would be inflicted by the amount of carnage D&D characters likely encounter on their rise to even 5th level... but they are probably the exception, rather than the rule. Even in a non-murder hobo game, look at the amount of sentient beings you fight and probably kill in a published adventure. This is further compounded by 5E's refusal to make decent "one fight per day boss monsters", so you have to wear the party down with even more faceless mooks to get the 6-8 encounters it expects. That's a huge horde of prisoners to shuffle around the dungeon/wilderness, unless the party all agrees to a "catch and release" plan (and the DM works with them to not have it bite them on the butt).
Most of that depends on the specific character.
Ive played a Monk that was a lot like this subclass in theme, and I've DMed for an Avenger/Assassin whose backstory was having been brought to an epiphany by a mark who became her mentor, and she sought to atone for her "sins" by helping others find a better path.
In both cases, trying to stop other PCs from killing people wasn't an issue.
Firstly, we don't do the murder hobo thing, as a group. It's super weird to us, and I wouldn't believe it was even a normal/common thing if so many people didn't insist to me that it is.
Second, I have no idea what you're talking about with the PTSD part of the post? In a game with less bloodshed, why would you assume there is a lot of carnage? That seems contradictory, to me.
We don't solve every problem by killing people. We rarely shoot first, and when we do it's when it's clear there isn't another option.
We just....don't kill most of the people we fight? We don't assume that 0hp = dead, and we don't kill people that surrender. We treat their wounds if necessary and leave them or send them in the direction of the nearest temple, or lock them up in their own hideout/whatever and send for proper authorities. In adventures that aren't in civilization (most of our are, in the end), we just tuck them away somehwere safe and leave.
Because they are not in any shape to sneak up behind us and try to kill us again. It's pretty simple.
And the redemption guys make it simpler, bc they tend to have the skills to convince enemies to go home and rethink their lives.
About fights per day: it's a guide line. If it doesn't fit what you want out of the game, don't use it.
Or use social and exploration challenges to fill in for most of the encounters per day