With nonrenewable souls and rolling tied (as far as we know, perhaps swing speed too) to Soul Level, From Software would inadvertently turn this into a grind-fest. You'd carefully clear every enemy in the first area repeatedly until they're gone, leveling up as able, proceed to subsequent areas, lather, rinse, repeat.
You'd basically have to or you'd be seriously outclassed in PVP, especially if PVP is tied to time playing and not Soul Level. I'm overthinking a situation that's purely based on speculation; I'm an ass.