One stick climbing is not really all that different from climbing with multiple sticks. It does take slightly longer, and has a little more of a learning curve. But if you're sweating one sticking, you're not doing it right.
The single advantage of one stick over multiple is weight/packing. I hate carrying multiple sticks enough I won't do it. I've tried. Ain't happening.
Rappelling is separate from climbing with one stick, and it's mildly annoying they're lumped together as a single thing. I have no issue climbing down with one stick. I will rappel, if it makes sense for the tree, but most times I don't. The extra gear, and stowage, eat into some of the speed advantage of rappel. It certainly has it's safety benefit though.
On the topic of weight - limits are being pushed in the name of innovation, and to signal to other people you're in the cool crowd. There are practical boundaries on how light your kit can be, and still get you up a tree safely, quickly, and quietly. But if people don't push those boundaries, you won't see the innovation continue.
And, like everything, there's tradeoffs to consider - and you hit the nail on the head. Weight for comfort is one compromise I'm willing to make with the hybrid. The penalty ends up being 1-3lbs. In exchange, I can sit dead still for extended periods of time.
Most people evaluate their kit through trial and error. They try different equipment and tactics, giving and taking what makes sense for them.
To answer your question- yes weight matters. To what degree, and with what tradeoffs, are not only individual and quite subjective, they're dynamic in that it can change from hunt to hunt.
If your point is that 3 lbs won't make a material difference in how many deer you kill, I probably agree. I would just remind you that there are likely blind spots in your perspective, and sacred cows you tote in the woods with you as well, that have no bearing on whether your success goes up, either.
I think the limit for me is this. If something takes away from my focus from the time I leave the truck until I return from hunting, or makes me less comfortable while I'm in the field, or less effective, that's the line. Tinkering in the yard, and trying gear at home, and playing with different methods doesn't hurt anything. Laying all my crap on a scale to see where I can pinch out unnecessary weight doesn't hurt anything. As long as it doesn't make me a less focused effective hunter during my time afield.
