I can understand his reasonings, even though I don't fully agree with them. Like you said, backpacking is different from survival, so they don't neccessarily need the same equipment. From what you've described, it sounds like Chris is more of an ultralight backpacker, rather than the average backpacker. It's just a different mentality, you carry less weight, but you do trade off comfort and/or security during an emergency. I know some people would say with enough knowledge you could be just as comfortable and secure, but go backpackig with an ultralighter and see how often they keep borrowing your stuff
. I keep trying the ultralight methods of cutting pack weight, but a lot of times I'm just not comfortable with the tradeoff so I end up going back to my old ways.
My thoughts on some of these.
Water filters - I carry both filter and chemical tablets for emergencies. I've only used the tablets once (a long time ago), and from what I remember it tasted pretty bad, and you had to wait either half hour or an hour before the water was safe. I like having instant clean water, so I'm willing to carry the weight of a filter. Also, in North America, the risk of viruses is relatively low, so that's not a big problem.
Knife/Multitool - Depending where and when you backpack, you could probably get away with having a tiny swiss army knife, or sometimes no knife at all. Not everyone is chopping down trees while camping, and there are very few screws and bolts and cans in the wilderness, so multitool could be considered overkill. I still carry mine though, because I feel more secure in case of emergencies. I would honestly say I could get away with a tiny swiss army knife 95% of the time, for the other 5% makes multitool earns a space in my pack. I usually also carry a 5" fixed blade, but I don't think I've actually ever really needed it, but then I've also never needed my first aid kit either.
Sleeping bags - Never tried them, but I know a some of the thru hikers on the AT use a down quilt, which is essentially a bottomless sleeping bag. Maybe he just had a bad experience. I use a down bag with continuous baffles, meaning when it's cold I am able to shift almost all of the insulation to the top where it does the most good, or if I don't need it, I put it on the bottom.
Like OBG said, opintions are like noses, though I've always heard it with a different body part. Some people don't mind the tradeoffs that come with cutting weight, people like me like the comfort and security some of the equipment provides. I'm sure I could survive without most or all of it, but the whole reason I go backpacking is for fun, not to try and survive.
If you liked that book, have you ever read "The Complete Walker" by Colin Flether? I see they came out with a couple new editions since i read it, but I remember it was one of the best book on backpacking/camping/hiking at the time.