I can testify from personal experience that those unprotected hands have some advantages, if one does not go into the battle of armored lines. It gives more mobility for skirmishes and duels, and it is enough to complement it with leather braclet with iron bars. Rather, I would argue that armor is mostly impractical for fighting monsters. A lot of mnonsters (like a griffin) will have strength and claws equivalent to anti-armor weapons (like spiked warhammers) so the primary goal should be to not get hit, so speed is more important. (It's a similar idea as in the Witcher books - i.e. why is it not worth it for a witcher to wear armor - if you get hit, you're already doing something wrong, and in the case of a fight with a monster, the first hit is realistically also the last, regardless of the armor). I find this particularly disadvantageous if there is strong healing magic in the given fantasy world. Armor is intended against human opponents, and especially in cases where the battlefield is tight, so there is not much chance to dodge or parry their blows.
I actually mostly agree with you. I have read the rest of the manga and it reinforces in my mind, that armour is mostly useless in the context of the dungeon. The availability of healing magic as well as the supernatural nature of most opponents means that armour is essentially worthless against most of the enemies one might actually face.
I've finished the manga now and I did get to the explanation you're talking about. However, in my opinion, the rest of the manga sort of reinforces the idea that armour is mostly useless. There's barely any times I can think of where a character wearing armour or not would have been useful to their survival. Especially since it establishes early on that resurrection and healing magic is quite prevalent.
