If everyone doing right in their own eyes was God’s system, we wouldn’t need Judges, nor a Book of Judges. There was nothing right about Micah’s idol shrine for hire (Chapters 16-18) or the Levite’s civil war against Benjamin (Chapters 19-21).
If the Judges wanted to present this as quasi-anarchy as God's design, it's strange that every cycle in the book follows the same pattern: Israel does evil, is oppressed, cries out, gets delivered, then relapses. That's not a portrait of a functioning system. Rather, it's a portrait of a feedback loop God kept mercifully interrupting.
It’s also worth mentioning that the people of Israel weren’t actually a law unto themselves during this period. They had the Torah given at Sinai, a priesthood, the tabernacle, and judges whom God himself raised up to lead and adjudicate (Judges 2:16-19).
The trajectory of the book argues against this reading too. Judges ends with Israel in moral freefall, and the canonical narrative moves directly from there into 1 Samuel, where Israel's request for a king is treated as a response to real dysfunction (even if also partly a rejection of God's kingship, 1 Samuel 8:7).
If "everyone doing right in their own eyes" were the intended arrangement, the biblical narrative's own verdict on the period: chaos, idolatry, and a near-genocidal civil war, makes for an odd advertisement of it.
But why stop at 1 Samuel!
One of the clearest rebukes against everyone doing what is right in their own eyes is a verse near and dear to everyone’s heart here: 2 Samuel 12:7-8.
Nathan’s words to King David, and indeed, every prophet’s words to every person, is utterly devoid of any real meaning or force whatsoever, if people are merely a law unto themselves.
Reproof, rebuke, exhortation, all of it becomes vanity and meaninglessness in such an anarchic, supposedly God approved system.
"Thou art the man" isn't persuasion by reason toward a conclusion David is free to reject if unconvinced; it's an accusation that presumes guilt under a law David didn't get to write or waive. If moral authority terminated at the individual conscience, the correct response to every prophet in Scripture would be "thanks for your opinion," and the text would have no categories for the hearer ever being culpable for rejecting the message.