Wander makes some fair points above.
My warbonnet blackbird hammock and suspension weighs in at around 1.2kg and the down underblanket 0.8kg, compared to an inflatable exped xtherm mat (large) at 0.7kg and alpkit hunka xl bivvi bag 0.5kg, so 2kg for the hammock stuff and 1.2kg for the ground set up.
Sleeping bag and tarp would be common to both set ups of course.
So not really much in it in reality, and the volume and weight of a fitted bug net in reality I suspect is minimal too. The hammock is a double layer one though and is available in single layer and lighter material which would be lighter still.
Again as Wander mentions, another option could be a one man tent like a hilleberg atko or fjallraven abisko lite at around 1.6kg and you would only need a mat and sleeping bag, but very expensive for those models. Cheaper ones are available of course, and lighter ones, but I'm not sure on weights and some cheaper / lighter solutions are single skinned and prone to more condensation, these might come in around the weight of a tarp perhaps.
So I think that summarises to something like this -
Hammocking
Hammock 1.2kg
Underquilt 0.8
Tarp (DD 3x3, pegs, line etc) 0.9
Sleeping bag (Snugpak Elite 3) 1.6
Total 4.5kg
Ground system
Tarp 0.9
Sleeping bag 1.6
Mat 0.7
Bivvi bag 0.5
Total 3.7kg
Tent
Sleeping bag 1.6
Mat 0.7
Tent 1.6
Total 3.9kg
Obviously there are massive ranges of different products and I'm most definitely not a light weight hiker so don't get too hung up on the actual weights of the individual items above, they just happen to be what I use and I know the weights, rather it was looking at the kind of differences between systems in total, and I don't think they are really all that far apart ?
There's probably other ways of looking at it all too though and I may have missed some aspects possibly, interesting to stop and think about it all though