Any recent news, has anyone bothered to test this out in recent time since last comment? Or has anyone obtained info from some other servers like German, US, or same CH and other Asia servers?

I just tested, but I didn't made a long test, it was a short one, and I know that's not how testing works anyway, but for fun I did it.
Basically I left my 4th A and my main, stripped down everything from A, and didn't used buffs given by Lightning main in order to leave A as fresh as I can, and I only left Damage reduction. Don't take me seriously, like I said, hardly can be called a real test. But, enemy had Rosh etc, I made him to take off everything as well from Roshi and leave him fresh.

My rune is Sand 9.lvl (damage reduction obviously), yellow/golden. It gives +739 points. At clean, A has 1927 points at damage reduction, with damage reduction rune he has obviously +739 = 2666 damage reduction points. Pretty high increase, right? So it should maybe affect something that should be visible, at least by little.

So first I tried with having equipped that rune.

At first Roshi did 370-430 damage mostly, and I had equipped rune. Enemy had water main with poison, so Roshi did both fire and poison damage to my A. Poison did around 6k damage, didn't saw fire since poison numbers were over the fire numbers.

Next time I removed rune, funny thing was that Roshi now dealt 100 less damage, as if rune has opposite effect of sort :D but we all know this game is bs RNG at certain times. And poison + fire damage was less as well, kind of significantly less after I removed....................pretty weird, right? I mean, it wasn't just TAI damage that was reduced, but poison and fire as well in the same match as opposed to the previous when I had equipped that rune.

If we assume that there might be a bug hidden, a glitch in the code, and it actually does the opposite? I mean, people have tested it and they do not point out anything weird like that, but only the average, but I don't know, I am running 4x of those damage reduction runes, one for each ninja, raging from level 7 up to 9, all are golden/yellow.

Atm I have nothing to replace them with, so kind of stuck.

And with the translations by OG from German servers is weird as well, can't really trust, so I am still unsure whether that rune theoretically supposed to reduce overall damage, or it's damage that you deal to yourself, like, there's only one ninja who basically does that, and it's Hidan, with some exceptions having cursed mark ninjas combined with Kabuto, who damages each round all these cursed mark ninjas, but that damage is super small anyway that it just doesn't matter if he does it.

So theoretically it is supposed to reduce over damage incoming from enemy. Going by this bold translation without details.

He does not perfectly explains it, I came here from that video to do a research because there was no confirming answer. Just because he is a youtuber you shouldn't take everything what youtuber says as a fact unless really explained to why. He is basically saying the same thing what the guys are discussing here, that there is no actual proof at this moment whether or not these other attributes gives any kind of actual practical bonus or help.

BTrue thinks its true, he thinks people have done research, but he is basically basing his opinion on those people who have supposedly tested it, same people who are being mentioned here as well in above conversation if you would care to read. You see two sides conflicting about what whether it's true or not.

So BTrue is not explaining anything to why since he hasn't done a deep testing himself, he simply read about some stuff, maybe the same posts in which we are in and just read this one guys opinion or statement without much of a proof.