Yeah, that's a wide scope to view the subject with. But if we reduce it to backpacking it might be easier to compare if you focused on gear and techniques and the level of comfort derived from them vs effort to employ them. For me, that's an interesting subject, and one that spans time too.

I've read a lot of history on the european and american explorers. They all endured their hardships, but those arctic explorers really stand out to me.

It'd be hard to argue that any particular place or time took more toughness than another, it really has more to do with how I'd imagine I'd do in their shoes, so it's certainly not objective, but those Northwest Passage explorers got themselves into some really big messes and more than a few managed some amazing escapes from them. For them, it was a pure struggle with nature as opposed to more of a struggle with civilizations in an unknown land.

Unlike the european explorers of the lower americas, being brutal offered no advantage to the arctic and sub-arctic explorers, so they were of an entirely different kind of character. It's hard to imagine any of them trading places. Cortez and his men wouldn't have had a chance in those conditions.

As it relates to backpacking and exploring, both time and place still, right now, require different personal characteristics to endure the hardships one may encounter, and the "toughness" required is not the same for the locals who are acclimated and know how to get by in their local conditions, as it is for the outsider.