craig, you're talking about the same thing I am, only I think you're thinking climbing as a word means having tons of gear, it doesn't, it means you are engaging in climbing steep things that if you fall off you will get very badly hurt, as you say here:
"James and I were climbing pretty close together, communicating regularly to stay out of each other's paths for fear of dislodged rocks. The fact that we were in earshot of each other for the entire climb added safety, not insecurity, in my book."
See your words there? That's the climbing I'm talking about. If you mean something other than climbing your words should reflect that, or it gets too confusing. Once I am using my hands and feet on a descent/ascent, I consider it climbing, more or less, and maybe an order of magnitude more dangerous than backpacking itself. Not my thing, as noted, I've met one too many maimed people who have been airlifted to safety who do that sort of thing to find it appealing, but each to their own.
I understand what you are talking about, every time I've gone off trail for any reasonable amount of distance, I end up doing something I'd consider climbing quite soon. Just because someone engages in climbing type high risk activities while backpacking doesn't make it not climbing, it's climbing, and I agree, those type of high risk activities are different in kind, and require a different approach, as you correctly note, ie, they are not really appropriate for solo stuff as a rule, unless... they are, I guess. Skurka seemed to do ok beyond some boredom and loneliness, so I guess it really depends on the person. So did Lars Monsen, who also crossed Canada off trail mostly all by himself.
You used the words climbing correctly to denote climbing type activity, there's no other adequate description, and that's why I agreed with you, and will agree again, when you engage in climbing type activities, where serious falls will probably require an expensive tax payer subsidized helicopter airlift out as the actual final plan b, you certainly need to take the proper level of care, including having competent companions to avoid that plan b outcome. Personally I find it more interesting to do whatever, but accept that death is the price of failure, then to tailor my actions to that reality.
So you're correct to note that not all actions taken while wearing a backpack are best done solo, and to remind readers of this thread of that, although 99.9% of the readers aren't going to be engaging in that type of activity.