Most of the problem relies on things that you can 'make yourself believe' and others that you just can't. For example:
Any CRPG requires a very high suspension of belief.
Few example:
[*] A good example are the numerous fighters you kill and you cannot get any of their armors and weapons as if all was always broken. Unbelievable, but why you didn't quote it? I played a game dropping all and that's very tedious because of he amount of drop it generate, realism doesn't make the right choice for gameplay.
Ideally you should be able to get stuff from corpses, I agree, but since it's not something that's visible like the barrels, it's easier to ignore. You could also say that most brigands you find are just using broken pieces they've found here and there, so they have no value.
[*] You cannot attack any NPC, very low realism, but allowing it generate a nightmare to keep quests valid. Or worst for me they generate out of context message warning you that if you kill this NPC you could break the main quest, for example Morrowind.
For that I do have an explanation. In real life I can attack anybody, but it just doesn't cross my mind, I have no reason to do it, and even if I had reason, the consequences are so bad that it's almost as if I couldn't attack them. In game I just think that they are people I just don't have any desire to attack. Not a problem as far as immersion breaking goes.
[*] You are attacking a castle, but then you need some shopping, leave for a long travel and few days and come back continue the attack as if it was the second after you left it.
I do have a problem with this, and in fact, I almost never do it. I usually stick to one place until it's finished.
And I can add ton more so my first point is that you are making such an affair of one point the barrels which is quite a detail in comparison with many other very high suspension of belief a CRPG requires.
The problem with barrels is that they are so blatantly visible and being able to break them in front of everybody, and them having whole ducats in them, it's like worse than finding a Coca Cola bottle inside!
The second point is if like RivianWitch, I like opening a lucky-packet and I feel it adds to a deep exploration. I couldn't deny it could have been tempered a lot.
That point is that it's really a detail for me and even find few plus from it. And I feel that for example, the radar mini map is a much weaker point of the game, the barrels is a very minor weakness in comparison.
See I don't have a problem with the mini-map at all, I find it perfectly explainable. You can see NPCs there, which would correspond with your party's "streetwise" skill, same with the herbs and your 'Plant Lore'. The skill of your characters determine what you can see there. Even if there were arrows pointing me to NPCs, to me it's just the UI feedback for my characters asking people where to find person X. Very different and not an immersion breaker.
And if for the radar minimap you justify it from unexplained magic then consider barrels as the same, a magic move letting the hero unseen and uncaught. And yes it's limited magic working only for barrels and chests. And then, magic anyway not more than the radar minimap.
No, it's not magic, it's just a representation of my characters' knowledge/abilities.
But, hard as I try, I just can find no possible explanation for having a guy standing near his locked chest and then some random guy comes, picks the lock, opens the chest, and leaves with your armor, and you are just fine with it, or a barrel in the middle of town, some dude comes and smashes it, and hey! 10 silver pieces and a pommel in there, who would have thought?
It's all subjective of course. For example, people keep telling me to play Guild Wars, but I just can't. I tried, and realize it may be a fun game, but the whole 'choose your 8 skills for the adventure' just destroyed the game for me. So, I'm a ranger, but if I want to use my bow, I need to 'forget' how to wield my sword, or keep my sword but just need to leave my dog at home, or don't bring the amulet to resurrect people. It's a pure gameplay mechanic that destroys any sense of immersion. I guess the barrel thing is something like that.