What is the difference between the legalism of the Warring States period and the modern idea of the rule of law?

The Legalists advocated the rule of law, which is based on the principle of hierarchical rule by "power, art and influence". They emphasized "punishment for punishment" and "heavier penalties for lesser crimes."

If you stole something, you could be beheaded, and if you killed someone or committed a more serious crime, you would be beheaded.

There is a big difference between this and the current "rule of law", where a serious crime is used to deter people, and an appropriate penalty is used to give a warning.

As for the centralized power system, it is also very much related to the Legalists. The Legalists also centralized all power to the king. It gives the king the power to punish those who break the law.

The Legalist "rule of law" was to use heavy penalties to deter others, in order to achieve the effect of punishment to deter others.

And now the "rule of law" is more to protect the rights and interests of the victims. It also allows those who have violated the law to have the appropriate punishment, in order to with the warning.