This is the only part I find suprising:
Rocky sections - Kona quicker (possibly due to my knowledge of lines?).
Did you follow the same lines on the Five? If you are having to be nimble to follow the same line then it makes sense. Or, was it quicker to pick a line on the Kona than crash through on the Five?
Your summary of the Five feeling lazy reinforces what I see as the purpose of a bike like that. It's to take anywhere, do anything, all day then go do it again tomorrow. The Explosif is a thoroughbred race whippet; it'll get you from A to B fast, but I wouldn't choose it for an epic or want to ride it hard two days in a row.
I love the nostalgia of a one off ride on an old steel bike. But if I was riding seriously and regularly I'd want the comfort and versatility that something like a Five gives.
I think that subliminally I chose lines on the Kona which I know work for a hardtail. Using a hardtail makes you look for lines I reckon, whereas the FS option allows you to let the bike suck up the hits.
I think you are spot-on with the intended uses. However, I'm not sure that people buy FS bikes for all day work in general. A full day on the Explosif in that terrain gets more painful as you get older too.
I seriously don't think you need 5" of travel for most uses.