It is ridiculous both conceptually and mechanically, and it completely trivializes the middle-game.
Conceptually, if you are a nimble person, then the lighter your armor the more likely you can move your body out of the way so as to be less seriously injured by a blow (given the same armor). Say a berserk orc comes up with a 2h axe and does an overhead chop. If you move only slightly and it comes down on your collar bone--probably dead--if you move slightly more and it lands on your arm, you might get a very deep cut but live.
Unless you mean that the lesson we should take from it is to stay at least two tiles away from any moribund berserker who has an infinitesimal chance of one-shotting a bro.
Specifically what I said was if you can get the same tactical advantage while keeping him two tiles away, why take a 0.02% chance over a 0% chance? If you could not get the same tactical advantage and would have been in a much disadvantaged position, then the 0.02% chance is probably worth it.
Of course, the history of war was made by legions of peasants in rags being able to torque their body just enough to avoid death from a halberd.
Jokes aside, no, its conceptually ridiculous, since it works just the same if you are surrounded, if you are exhausted, if you are bleeding to death, if you have a broken leg + cut achilles + injured kneecap + concussion, if enemies have backstabber, etc. etc. etc. It's not tied to anything, and it works under any circumstances. It's basically Ultrainstinct, and just as dumb.
As I said, sarge had to be there exactly in order not to be squashed by another mansplitter berserker who had no shieldbro engaging it (but was killed, with some luck, after I had moved the sarge two tiles away).
Besides, the point is not that I lost a bro, but that it probably came from an AI brainfart. If came from an algorithm that has enemy units prioritizing inflicting damage when they are about to die, then it is a pretty idiotic one, since it would have made much more sense trying to wound the shieldbro, since it certainly had a much greater chance than 0.02% of achieving that (without risking a 93% sure death just in order to disengage).
That I was salty about losing the sarge has to do with how the battle took place: I had the 5 berserkers + 1 young coming down the mountains, saw them at the last moment (which is fine, that's what elevation is for, even when it works in favour of the enemy), backtracked immediately, my party started going zig-zag on the hills for no reason, and while clicking frantically in order to try and make it go straight I got snagged while being just between a plains tile and a hill tile (with the mountain tile being just next to the hill tile), but that apparently counted as a mountain tile, so I got caught. And as I said, I usually reload when this kind of things happen, but that doesn't mean I don't feel slightly guilty about it, so this time I said "ok, I will retreat manually". Battle starts, and two of my bros are with their back to a two level cliff, and if they go around it they will be caught by orc charge in turn 2. So it's "fine, backs to the cliff, and we go down in a blaze of glory". Turns out than it was much more glory than I expected, but then I just played, you know,
suboptimally by not leaving the sarge in the range of the other berserker with mansplitter (who would have got him in case I missed one of two javelin shots), and moved him one tile away from a moribund, breaking berserker being checked by by best tank.