To me a linemans belt is both prevention and protection. While I have never truly fallen while using one, I have sat in them without the support of steps many times (sometimes pretty aggressively while demonstrating their use), and have found they reliably stop and hold within a foot or so, maybe a bit more if I've let slack build up as mentioned above, but also remember it's a "slide" as much as a "fall". It's not crazy comfortable, it's likely to leave some embarrassing scrapes, but they've held me reliably and I'm confident mine will prevent a catastrophic injury should I break a strap or a step or something like that, and that small risk is fine for me given the extremely low likelihood of a fall. Im also confident one could concoct a “worst case scenario” where a linemans belt would not provide the level of protection I desired, but having used them literally hundreds (maybe thousands?) of times I'm pretty confident that unless I'm intentionally trying to contrive that situation it has about as much chance of happening as me getting hit by a bus—it could happen, and therefore I look both ways before crossing the street (i.e. diligent attention to managing my linemans belt), and at some point I just have to decide when I've done enough to keep myself safe and put the rest in the hands of God, fate or luck. I dont need or want a backup to my backup, and I think that hypothetical situation is so infinitesimally low-probability that all those factors line up just the wrong way simultaneously, that I simply think it's a waste of my energy to try to anticipate and prevent it from happening. Using a rope AND a LB would be redundant and involve unnecessary complication and hassle--for me at least, it's extra fuss, weight, etc without adding enough additional safety to matter. I also feel the additional complication and fiddle-factor involved with doubling and tripling overlapping safety precautions creates the potential for as many safety problems as it alleviates, to say nothing of adding enough weight to your pack to in some cases subvert the whole point of a mobile setup in the first place. YMMV, and I often carry two headlamps for a reason.
Yes, you can always set up after daylight, or you could only set up in trees that you have pre-prepped with a cord to pull up a rope, or even a pre-rigged safety line, but that significantly limits when and where I can hunt and simply does not work for me, and frankly I don't like the idea of littering the woods with pieces of paracord that I may or may not come back to retrieve. Same with using both a rope and sticks—a rope is SOP for a fixed stand, but throwing the safety rope before climbing a set of sticks is limiting to me in the same way a climbing stand is (gotta have that particular branch...), plus adds complication , bulk, weight, noise/commotion and hassle, without adding enough additional safety compared to a linemans belt that I see a point. If you or someone is more confident doing that, by all means do it where you can. The whole point of having a mobile setup for me is so I can hunt new areas, look for sign and set up on it “in the moment”, ie totally un-prepped and as much as possible unencumbered, with as much flexibility as possible to set up exactly where I want regardless of what tree happens to be there. It is never going to be as clear-cut as any fixed stand since every tree and setup will be different in ways that you cannot always anticipate--you have to have some basic tools and know how to flexibly use them in a way that is safe-enough for you, in a variety of different situations. If you are setting a couple stands or prepping trees ahead of time, absolutely use a safety rope and whatever tools are available to add safety and efficiency...that's just not the situation I'm talking about.
Most people I know can recognize a buckled and tightened cam-buckle, but very few recognize the difference between a properly tied prussik or klemheist knot versus one that's going to slip, or replace or readjust one after it falls off after a moment of inattention, or tie and adjust a harness so ascending is least strenuous, etc--I believe this is a big part of why the mechanical rope-grabs are so popular for a tether. Climbing with sticks is literally as simple as strapping the stick around the tree using a cam buckle. Slip the loop over the button, tighten the buckle, set the stick by forcibly jerking it down, stand on it. Clip linemans belt to the loop on your harness on one side, pass around tree, clip to other side, snug it up so you can comfortably lean back on it without leaning far. lean back, set next stick, stand up on it. Move your linemans belt up with you as you climb. lean back, set next stick. repeat, add oregano, serve. If you pull up the second stick using the strap, and hang the other 2 sticks off each side of your harness, there is no need to go up/down/up, you can be almost totally silent, and be up a normal tree and hunting in well under 10 minutes without needing to practice excessively or work up a sweat. When done, reverse the exact same process. Even my amsteel daisies, while some people dont like them because they dont tighten as securely, dont even involve a buckle at all--if the loop is over the button, it's on...with the caveat that it needs to be diligently set to be secure, I'm not sure what could be simpler.
From reading the posts I cant tell who has used sticks or JRB or both in the past, and how much--but for anyone still reading who hasnt used both extensively I would encourage you to find a friend locally and swap gear to try this stuff out together--prepping a couple trees in the off season on a hot day in july is a great way to do this--and with the benefit of someone who's practiced to show you their method, see which ways are easier for you to climb without breaking a sweat, which are quieter, which are faster without rushing, which are easier to tell if they somehow got effed up in your truck or pack, the degree to which each protects from a fall, and make your own decisions.
Again, if anyone feels they are more comfortable with any other method, or have a specific reason they want to move away from sticks (especially if it's borne from personal experience), or they just want to do something different, GREAT; just don't fool yourself into thinking there are huge, glaring inherent problems with using sticks and a linemans belt to get up a tree and manage your safety in a mobile tree stand setup--there arent. They may not be perfect, and there are many types of them as people have tried to keep making them better, easier, lighter, etc, but there's a reason that 1) sticks + hang-on or saddle or 2) a climbing stand are the standard setups for mobile stand hunting that all other methods are measured against.
edit: also, not clear if the OP is looking to have a mobile setup or just pre-rig a couple stands. If pre-rigged I would use cheaper sticks/ or a strap-on ladder and a linemans belt to hang it, and leave a fixed tether that reaches almost to the ground for future when you climb it to hunt. If you are in the typical plains stream-bottom cottonwood like I'm familiar with its likely there arent many accessible branches you would hang a rope from anyway. You can leave the top couple sticks in place and just cart the bottom stick in with you if you are worried about people messing with your fixed stand.