This is a remake, not a new Souls game made by a new team. The aesthetics are obviously important. If you'll forgive a bit of hyperbole, would it be the same game if they kept the mechanics and level design intact but replaced the art with steampunk theming? Or replaced the soundtrack with licensed music? What if they left functionally everything the same visually, but they rewrote the lore entirely? Some parts of the aesthetics are even inextricably tied to the gameplay! Maneater(s) would be an entirely different fight if it took place at high noon. The "kind" of game would be the same in all of these scenarios, but I'm sure all of these changes would be seen as indefensible.
I'm not saying that they shouldn't be trying to match the gameplay so closely. I'm glad they are! But I completely disagree that it's somehow more important to the soul of the game.
I also think it's somewhat irrelevant that the original art was informed by the hardware. Yes, hardware limitations and budget were likely a big influence even from the concept stage. It's entirely possible that enemies like the Fat Officials had inhuman, permanently affixed grins and cloudy, death-like eyes because they didn't have the resources to bother with facial animations. The relative lack of vegetation in Boletaria proper is probably another one (though it is worth noting that the outskirts in the tutorial area had a lot more greenery even in the original game). But, to me, all of that is part of what made the game what it is. I'm not sure why better hardware means the Fat Officials are grumpy and covered in pustules now. Or why Boletaria is overgrown and appears to have fallen into decades of disrepair despite the collapse being relatively recent.