Deathwing and Muklah both are very strong in the midgame, making it very common for them to place in the top 4. That’s why they are rated so highly. If you want to gain rank, they are very good picks.
Deathwing in particular can just run some deathrattles and it’s almost impossible to do better than tie him on turns 5-7, meaning he also can power level in some lobbies.