I think the damage ratios and resulting difficulty go way up, fast, at about level 15.
Im saying that, because i'm currently trying to clear out the deathclaw quarry at level 17. None of my guns seem to do any good damage against full sized d-claws, and they kill me in 2 swipes... =/
Once I hit 15 I also had a dead end save where I was cornered by 8 caesar's ppl, I tried over and over, keep getting owned, guns do no damage.
This is on medium, with at least 60 points for the skills of the guns im using (plasma rifle, 44 mag, caravan shotty mainly).
It's a common thought the one that expects difficulty in F:NV to change with the your level. I'd like to clarify that a little here, since the thread deals with two different cases.
NPCs/Creatures in the Wasteland, in areas that are not necessary to vanquish to advance the critical path (read: the vast majority of the Wasteland), are not leveled relative to you. They are also not spawned from lists that change according to level. They are what they are, consistent, and persistent. You may notice that remote, harsh locations (mountains, areas far away from urban centers, etc.) tend to be inhabited by creatures much more fearsome than those found in relatively "tame" areas of the Wasteland.
In contrast, enemies that appear along, or at specific challenges of, the main quests' paths will change in difficulty depending on your own level.
So, while the Legate indeed changes difficulty depending on your strength, Deathclaws at Quarry Junction will not.
My advice? The Legate is a tough-as-nails man. Use every trick in the book against him, and you'll prevail.
O.