The existence of unknown rightmaking properties does not undermine the evidential argument from evil, because unknown wrongmaking properties are equally likely and would counterbalance them.
Counterbalance(as used in this thought experiment)
To weigh equally against something else, or to cancel out the effect of something by being just as important or strong.
Evidential argument from evil(in philosophy of religion)
A philosophical argument claiming that the existence of suffering and evil in the world provides evidence against the existence of an all-powerful, all-knowing, and perfectly good God.
rightmaking properties(explaining what makes an action ethically justified)
The features or characteristics of an action that make it morally right or good.
the problem of evil(Contemporary philosophical terminology)
The family of issues raised by the question of why pain, moral wickedness, and varieties of imperfection exist if a perfectly good and all-powerful God alone created everything in the universe.
undermines(as used in argumentation)
Weakens or damages something by removing support for it or showing it doesn't work.
wrongmaking properties(explaining what makes an action ethically problematic)
The features or characteristics of an action that make it morally wrong or bad.
When the argument from evil is formulated in this way, it involves five premises, set out at steps (1), (3), (5), (7) and (9). Statement (1) involves both empirical claims, and moral claims, but the empirical claims are surely true, and, setting aside the question of the existence of objective rightmaking and wrongmaking properties, the moral claims are surely also very plausible. The other four premises, set out at steps (3), (5), (7) and (9), are plausibly viewed as analytic truths.