A couple extra cards have tipped plenty of commander stalemates, and lets be honest, a surprise Molten Primordial or Resolute Archangel is not only fun to pull out, its going to screw up combat math in a big way
Most other mass removal spells in Standard right now either cost more mana, have some sort of stipulation on them that gives your opponent something in exchange for blowing up the board or just isnt as efficient as Day of Judgement
As his last wish he asks her to take his life
Whether it's killing a bomb of a creature definitively and turning the tide of the game, or comboing out with Jaws of DefeatJaws of Defeat to take a player out, Overkill will seldom be unimpactful in a game of Commander
Price is difficult to justify for casual play
While being limited to larger creatures is pretty ruinous for both Valorous Stance and Reprisal the added utility of this Charm offsets that pretty perfectly