What system, in your world, is not malleable and ripe for corruption? In your world democracy would be the most malleable and corrupt while autocracy would be the least given the boundaries you laid out.
In autocratic regimes justice is usually perverted from the top (comrade district secretary calls district judge to affect proceedings - in USSR it was informally known as "phone law"), in democracies you usually need to involve wider public pressure to achieve similar results. It's definitely makes democracy better, because to sway public opinion is costlier, more visible and at least partially deliberative endeavor. But legal justice is not moral justice in any political system, and there are always ways to at least nudge legal system in a way that is more convenient for some forces.