To prevent a repeat of the Empire, the New Republic completely denied the centralized system.
The capital planet was decentralized, and many star systems became independent. It boldly promoted democratization, the exact opposite of dictatorship.
It significantly reduced the costs paid by the central government on Coruscant.
But is this really okay? It's fine in peacetime, but it will be weak in times of emergency.
If we face a security crisis, we will be weak because there is no central government.
Mon Mothma and Leia warned that it is dangerous to completely deny the central government. (Both of them were later ousted.)
On the other hand, even though the First Order is decentralized, Snoke is still at the center.
As expected, the New Republic surrenders in an instant during the invasion.
The decline of the Empire, the signing of a ceasefire agreement, and the death of the Emperor caused the Senate to downplay security concerns.
During the Republic era, there was a central government, so they were able to deal with the Clone Wars. A centralized system is necessary in times of crisis, but history teaches us that it should not continue forever. The Clone Wars dragged on. If it hadn't dragged on so long, the Empire would not have been created.
At the end of the Clone Wars, the Jedi recommended lifting the centralized system. However, doing so would have caused a sudden instability in the security of the entire galaxy.
The problem is not so much that the principle of centralization emerged, but that it dragged on for so long.
(There was little discussion about gradually lifting it or what to do after the crisis had subsided.)
Thrawn completely rejected dictators when he came up with decentralized governance.
The First Order Plan is a perfect system in theory, but having a dictator is better in times of crisis.
It is easier to respond to unforeseen circumstances.
Thrawn underestimated the risk of completely rejecting the centralized system. He was tired of the Empire's centralized system.