In terms of using a rangefinder in the field, (I haven't seen the video yet, and it's late here, so I'll be looking tomorrow) I think anyone choosing to use manual focus in that kind of environment is commentworthy.
I don't shoot in anything like those environments, the most I ever have to be on the look out for is the odd bottle or foot heading in my direction, but I know that I certainly wouldn't like to add in manual focussing to the things demanding attention. and I have huge respect for anyone who does.
There is a danger that viewing from the sidelines we can have an oversimplified view, and it's all too easy to write things off with broad strokes because of that. It's thanks to people like John that we get a view that's more relateable on a human level. Something we should be grateful that there are people willing to go out to places like that, and bring that view back.
It's also obvious that it takes a toll, hearing Don McCullen talk about his body of work, it's clear that as well as contributing to the world's understanding, it has taken a toll on him. It's one that's most often forgotten, because the "damage" ironically isn't so visible, in some ways it seems a much tougher subject to broach as well because of the non visible nature of it.
I just want to wish both John and Deejon the best in dealing with it, and recognise that it takes some bravery to be open about it.