I always reach Arx at lvl 18, and enter the crypt at lvl 21, in both DE and CE. If you do most quests and murder most magisters/paladins you'll get that. If you avoid the peace keeping forces you'll be one level below that.
Here's the thing, there's a few more fights in Arx in DE (mostly outside the city proper in obvious places as long as you look at the map), so the nerf wasn't actually a nerf, more a redistribution of exp.
Another thing about the "avoid this and that", for those having trouble, you can easily destroy mobs while underleveld by abusing the shotgun mechanics of these spells: pyroclastic eruption (dust blast for lvl 9~15), mass corpse explosion (if you can't find corpses, your party memebers will do lmao), thunderstorm and blood storm. The way it happens is that one shot is fired for each target, all of them with an area of effect, so if you teleport your enemies so they clump up, it'll hit every one with multiple times the damage it would against lone targets. As an example of how OP that is, I oneshotted the lvl 15 voidwoken harbinger east of driftwood at lvl 10, and the 2.5k hp kraken at lvl 18, with 5 corpses each.
