"But where status quo is also an expression of power, there can also be an onus to justify its existence."

That's literally every law.

"Which is all to say, the onus isn’t on anyone to unjustify something that’s wrong"

The onus would be to show that "something" is wrong for that logic to even apply. As you said "you’re making the claim, you defend it.". Society already decided that it was wrong and formed a law, so now it's time to hear why it shouldn't be (I'm interested in research on either side).