The amount of effort required to fix weapons "floating by characters backs" is not worth the time and energy cost for such an extremely minor thing. Just get over it, and save your energy for more important things.
You seem to be assuming that immersion and enjoyment are opposites, that inceasing immersion will somehow decrease possible enjoyment of the game. I think that is a false presumption. For example, how would the game be less enjoyable if weapons were carried realistically, or if there was a passage of time?
I think that in general, if done right, improving immersion will improve enjoyment. I think that everyone playing the game, perhaps some more than others, is in need of believing the illusions that the game offers: that there is a real world with real people trying to solve real problems.
I will give you that in some cases improvement of immersion versus enjoyment is debatable. For instance, personally I could do without the enormous amount of junk (and accompanying inventory management) that you can carry. (seriously: why are the people in the game so keen on having crates and chests everywhere when everyone can shove five cheese wheels, ten barrels and twenty sets of full armour in their back pocket without it even bulging a little bit?). But Larian should be clever and creative enough to not let immersion stand in the way of enjoyment. Whether they are willing remains to be seen...
Your thinking is incorrect, because not everyone enjoys the same things, and some things people find to be immersive can be frustrating for others.
For instance, it could be considered more immersive if instead of having fast-travel points, you just have to walk everywhere. But the more you travel back-and-forth across empty, cleared areas, the more it feels like a waste of time.
OK, but in combat everyone is holding their weapons, right? And in combat they are climbing, walking, running, falling prone, jumping, falling, attacking, blocking, taking hits, casting spells. So the animations are already there. It would just be a matter of having people hold on to their weapons outside of combat.
That is an approach, one that Solasta takes (outside of cutscenes - but in those characters just stand still), but the question is whether it would be immersive to be in a peaceful village running around with weapons out ready to attack at a moment's notice, and in cutscenes, not reacting naturally, but holding out weapons no matter what is going on in the cutscene. That does not sound like an improvement in immersion compared to "weapons on people's backs".
