My point is the mainland Eldians have shown dissent towards Marley rule, we know about two failed groups of them who have tried to oppose Marley, the restorationist group where Kruger family participated and Grisha group. The warriors too have shown disdain about Marley, Annie says they are full of shit, Porco dislikes the Tybur family and Pieck doesn't trust Marley either. It's false to assume the mainland Eldians are completely brainwashed, Marley has to constantly survey for any sign of dissent towards them and the fact they still send Eldians to Paradis for that, show their control is not absolute.
If Paradis ever wanted to restore Eldia, they would need the support of the Eldian population in the mainland. But after Liberio attack that bridge is burned without repair.