I have trouble believing that on a heavy barrelled 22 rimfire, that barrel oscillation is a significant source of inaccuracy. And that by moving the weight slightly alters that oscillation enough to improve accuracy. I can readily accept that on a high pressure centre fire cartridge, the barrel oscillates enough that finding a node might make a difference, but I am skeptical about a heavy barrelled 22 rimfire. I remain open minded, but a better barrel and better ammo would do more for me than a tuner (I speculate!).
I appreciate your expression of healthy skepticism, and keeping an open mind. A wise man knows that he knows nothing. It doesn't really matter what anyone tells you, there is no substitute for seeing it first hand with your own eyes, that is the condition in which one genuinely learns something. You just haven't had the experience yet, that is all. My PRS rifle has a 0.900" barrel, I've got some ammo that will string 4" vertical at 100 yards in it. This ammo might not be the best, but it'll shoot 1.5"-2" groups in other rifles. What else explains this ammo in that heavy barrel stringing vertical so badly? If you didn't live so far away I'd invite you to the range to see it yourself.
There is a clear consensus on tuners, but there are also quite a few loud voices out there muddying the waters with ignorant views. It makes for a very confusing environment for one to dip their toes into. If one sticks with it and tries out many things, eventually something should click and things will start to make sense. It comes back to that first hand experience thing. I don't have a magic formula to offer anyone, I'm only experimenting and hoping to find something that works myself. Come up with an idea, try it out, see what the results are, come up with a new idea and repeat. Sometimes people will give up on it before figuring it out, and in frustration they'll start saying things like tuners are a "myth". It's unfortunate that they feel the need to poison the well. Others might say tuners don't significantly improve groups. That is a misguided assertion and paradoxically, both correct and incorrect. In certain conditions, there isn't a significant improvement to be had, making the statement correct. In other conditions, a tuner absolutely can make a significant improvement, making the statement objectively false. There is also everything in between the two.
One thing I do know is that putting a random style/weight of tuner on a random barrel length/profile is unlikely to result in success. I haven't done anywhere near enough work to even begin to suss out what weight, and distance that weight should hang past the muzzle, is appropriate for the different barrel styles. If you try something and it doesn't work, it doesn't mean that tuners don't work, it just means that was the wrong setup for the barrel. There's a lot to consider, so be careful around those who loudly proclaim it's one thing or the other, they often don't have the experience and understanding to support what they profess.
