To whoop a deathclaw in vanilla very hard difficulty with melee + without VATS + sober. you will need following
1. level 24 with all needed perks
2. Chance's Knife
3. Shovel or Nephi's Golf Driver or 9 iron.
4. some good timing.
When you are face to face with it, 2h special attack it with any 2h weapon from #3(100% chance to knockdown), have to get used to the distance and timing though. if it uses normal 1 hand to attack you, your special is always faster. If it charges to you from far and perform 2 hands special on you, strafe sideway, 2h special attack from sides.
The idea is once it's down, it's down forever, keep knocking it down and swap to use Chance's Knife to slice it.
Unarmed special move Ranger Takedown can use this idea too.