No ax to grind, not promoting anything, but impressed with today's superlight equipment that seems to have come from the well-heeled quadrant of the thru-hiker world.
So, a bivy + a tarp lighter than a roughly half kilogram Zpacks Plex Solo tent?
Yeah mine can be a little lighter depending on which options I take. even though not real high dollar stuff. My bivy weighs 7 ounces (
Borah Side zipper ultralight bivy) and my bug bivy weighs 5.3 ounces (Ti Goat Ptramigan Bug Bivy). Which one I take depends on expected temperatures. My tarps vary from 7 ounces to 12.3 ounces. So my lightest combo is about 12.3 ounces and the heaviest is 19.3 ounces. The heavier setup is with a very generously sized tarp and much heavier than it really needs to be. I just like the luxury of the larger tarp.
Bear in mind that my bivies and tarps are not the lightest and most $$$. I don't own any super high tech fabrics so I could go a good bit lighter with the application of more $$$ for cuben fiber or whatever. Also I assume the tent you mention most likely requires a treking pole which typically isn't included in the weight.
I'd think it would be possible to stay down below a half pound if spending the kind of money the Zpacks tent costs on a tarp and bivy since that would probably get you a Dyneema tarp and bivy. That said, I haven't priced them lately as I don't find Dyneema worth the money to me.