I'm of the mind that any one of has to always have an immediate impact on the game, and that just isn't Doom Blade at this moment. I'm sticking with my cut.
Agreed, but Doom blade isn't strictly functioning as a one-of. It's part of an overlapping 2-drop removal suite with Last Breath and Ultimate Price that gives me early game against faster decks. Cutting it means I only have two functioning cheap removal and turning it into an ultimate price or last breath is cutting out relevant target potential for turn two.
Note that Mutavault is one of the most notorius targets for control players and cutting Doom Blade gives me one spell before turn 5 that can kill a mutavault. It also kills both Mistcutter Hydra and Stormbreath Dragon at the top end, and Fleecemane Lion in the mid-game before my naya opponent can monstrous or otherwise make indestructible.
Doom Blade is only irrelevant against an MBD player in the first game on the chance they never draw mutavault. Which is not entirely uncommon, but Mono Black has so few relevant immediate threats that changing around my 2-drop suite for the matchup at the cost of others is hardly efficient, especially when I'm dropping 2/3 of those cards for Dark Betrayals in the second game.
There's an argument for turning it into an Azorius Charm, but I like being able to hit SotP, Stormbreath and Mistcutter. Azorius Charm is also so horrendous against haste creatures that I stopped running them entirely. I run enough lifegain in the 75 that one charm will never be relevant for that purpose and a two mana cantrip isn't exactly what I'm in the market for.