My biggest concern is they picked the wrong attribute to scale.
Vicious Mockery should've been disadvantage on your next attack roll for each bracket, instead of adding in negligible damage each time.
So 5th level, 11th and 17th would've meant the next 2, 3 or 4 attacks the next round. The damage is too low to be used as an offensive spell in any circumstance, so it should've focused on why people really like to use it (since I used it this weekend to prevent 19 points of damage in a roll20 game and, in combination with cutting words from other sources, effect a 30 point damage swing on our Ranger (level 4) to ensure victory in the combat.
Which made up for the fact whenever I tried to use a weapon I was lucky to roll as high as a 5, oh yeah!