XUL vs. Survival vs. Adventure Racing vs. FUBAR

So I've been reading again lately on bushcraft, outdoor survival skills, etc., and I'm thinking "Hey, why don't I start taking more ULTRA minimal trips and practicing some of these skills?"
The idea of carrying VERY little appeals to me.
I'm not talking about running around and chopping down trees and trying to murder local fauna, but more along the lines of going for 1-3 night trips in which you're only carrying the "ultra" basics. I want to see how little I can get by with; I've done the SUL/sub-5 thing but want to push a bit further.
But that's where I start thinking in circles and want to open this idea to discussion…

So what are the "ultra" basics? What exactly constitutes "survival" vs. XUL vs. an adventure racing style (i.e. long miles, little sleep, little gear, lots of suffering) vs. being straight-up FUBAR and having nothing?

I was watching a video of a self-described "survival expert. He was carrying a Becker BK 9 (read gigantic knife) and a full-blown survival kit- space blanket, first aid, firestarting, water treatment, etc.
His justification for the giant knife was "building shelter".
Know if we're judging by weight, his kit's a complete failure. Why not skip the 2 lb. knife and carry a bivy and tarp and never worry about building shelter?
Now if we're talking being stuck indefinitely on a deserted island, I'd probably choose the Becker BK 9 over a cuben tarp and build some nice, permanent shelter.

But it just doesn't make sense…If your "survival" weighs in at 3-5 lbs, why not just never leave home without your SUL kit?

So is this about weight, having an ultra-COMPACT kit….what?

I suppose "survival" hinges upon being prepared to spend an indefinite amount of time somewhere, thus carrying items of long term utility/durability…

I was thinking I'd go out and spend a night or two practicing a more realistic scenario: getting lost/injured while on a solo 50K trail run and ONLY having what I'd typically carry trail running (my Nathan race vest, a space blanket, a small knife/first aid kit, firestarter, LED, some water pills, etc.) I'm sure this will tell if I'm lacking anything.

Or it will only tell me that spending the night in a space blanket under a makeshift lean-to on top of a bed of leaves is miserable, but survivable. Or more comfortable than I thought.

But isn't this pretty much just adventure racing?

Coming from SUL, having a well stocked survival kit sounds like nothing but an SUL trip without the tarp and sleeping bag.

So is the point simply pushing your suffering/comfort level? I think there is something to be said for doing this from time to time.

So maybe the best way to practice "survival" skills in the woods is just driving out after work one day and spending a night or two carrying only what's in your pockets…

I suppose the first question is "what do you really want to learn?"

Any thoughts on these ramblings?