Tarps are fine for good weather camping, but I will take my Tarptent Dbl rainbow for a hunt all day long. That setup kills a tarp in every way.
Tarp and ivy is not lighter and has no advantage only disadvantage. Just a tarp and you get wind, sideways rain, bugs, etc. Bivy gets you condensation in your bag, I must give off a lot of moisture, my bag gets soaked.
I dumped the bivy idea and the tarp idea 35 years ago and never looked back.