"The best thing about the SuperShelter, after you have mastered the learning curve, is the ease of augmenting it with very light weight insulation, some or most of which you might have with you anyway. For example, if you don't already need to sleep in it, placing your jacket or a vest underneath the underpad, in the undercover. Or spare longjohns/socks/dry pack towel on top of the underpad."
This is nice in theory, but in practice if I'm concerned about keeping warm, I'm generally wearing pretty much every stitch of clothing I carry --- makes it easier to get in-and-out of "bed" in cold weather. I'll have maybe a spare pair of underwear and socks to stick in there, which doesn't make much difference. The HH site talks about putting in dry leaves; where I live, if it's likely to be cold out, you don't find a lot of dry leaves or moss or whatever. It's possible, but not typical.
I'm not saying this to knock the overall idea that, yes, you can use various things to augment the underpad as part of the supershelter system. I'm just saying that in practice for me, it doesn't happen.
The space blanket does help, but is a bit of a PITA to put in at night and then take out and fold up in the morning; I'm not fond of the crinkling sound at night, and it can cause condensation.
To my knowledge, torso/kidney pads aren't available via the HH website or anywhere. You could no doubt get some open celled foam from a local outlet and cut your own. The open celled foam wouldn't likely move around (on top of the supplied underpad) due to friction, but just getting it in the right place to begin with --- I think most of us move around some as we sleep, dunno how well a person would stay properly aligned over strategically placed foam pieces.
It could well be that a hammock setup involving a JRB Nest could get (significantly) lighter than what I'm carrying; I'm not sure how, though, I think the JRB nest plus suspension system is something like 22 oz. The HH undercover plus underpad is listed at 13 oz, and I think that's about right --- I add a second underpad for 5.5 oz more, or 18.5 oz. The JRB nest is likelier warmer than the supershelter even with two underpads, but (a) I already own it, and (b) I think what I'm carrying is slightly lighter and (c) it will hopefully be warm enough for where I'm likely to camp.
Going the Spear route doesn't save weight, in fact it loses gound; looking at my notes from last time I checked, a Spear hammock + straps + tarp is 32 oz, peapod is about the same, so that sums to about 4 pounds.
It's tough to do a fair apples-to-apples comparison either between hammock options or between a hammock and a tent --- as everyone is different, we'll make different trade-offs, plus $$$ factors in.
For example, I tried going without a thermarest when tent camping, just using a pad, but after testing I went back to the lightest 3/4 length thermarest. A person who uses just a torso pad and wears a bug headnet under a poncho tarp will find any warm-enough hammock option (in my part of the world) a whole lot heavier.
For my specifics (gear, body chemistry, existing equipment options, geography, etc), the hammock route is about a pound more, and I'm hoping to narrow the gap a little, but ... I think it will always be heavier.