Actually, you don't need to divorce the level of Norvarandt beings from the story entirely. Like, yes, in places it's a bit out of touch with the story, but in all zones there is the reason that beings had to survive in a literal wasteland for a hundred years while Sineaters move about killing and converting everything too weak to resist.

This basically holds true in every zone, with the exception of The Tempest, but even in The Tempest, we can chock that up to the sea creatures that didn't die several moments after being completely deprived of their natural habitat, i.e. the strongest ones.

As for how soul density is affected, that's a matter of contention. Rejoinings will only affect the planet itself and life that contains souls from the ancient world. All new souls, regardless of shard, likely have similar densities, which are less dense than ancient souls.

Of course, soul density isn't the only determiner for strength, considering the gulf of strength between Catboi Sage Deluxe and the WoL. Or like how we start out at level 1 barely able to contend with squirrels. There's a whole physical aspect to how well bodies channel and direct their aether. The stronger you become physically, the better you are able to direct and control your aether.