Well, yes, it is quite powerful. Remember, this is a peer to Tiger Warrior Training - the Solar Essence 3 Charm that lets you spend a week to train up a dot to a maximum of 4, trains Essence magnitude at a time and only requires a few hours during that week of the Solar's personal time, and is a permanent Training effect.
This Malfeas one is balanced relative to TWT on the factors that:
- It's faster than TWT, but only lasts a scene so you have to literally massacre your own troops on the battlefield to encourage the others.
- Unlike TWT, it requires you to be there in person - that means you have to micromanage everything. That's a big deal - TWT lets you garrison your towns with civilians who fight like veterans. This doesn't.
- With the repurchase, you're killing a third as many people who benefit from it to fuel it, which isn't a long-term sustainable option.
TWT lets you produce an elite cadre who'll always be an elite cadre. This Malfeas effect can't do that - it lets you grab random less trained soldiers and civilians, execute some of them and send them out to fight like devils because they're more scared of you than they are of the foe.
(It also has a secondary function of letting you get some benefit from randomly executing people who fail you in day-to-day life, because it gives everyone around them +1 for the rest of the scene)