"Mole was Micah was all along"
You have added this headcanon again. Let's be clear.
Agent Milton never said that Micah was Mole all along. Here is the full quote "Micah Bell, we picked him up, when you boys came back from Caribbeen, and he's been a good boy ever since" proof: https://youtu.be/sN-DXNClTPk?t=282
So Micah has nothing to do with failure in Saint Denis and Blackwater. According to Milton, to the sixth chapter in the gang there was no mole at all. Simply, the world has changed and the law has become stronger, as we are told at the beginning of the game. And the gang continued to act brazenly, thinking that no one could stop their impudent robberies.
The most that Micah could sell to Pinkertons was the location of two camps.