A number of scenarios can be followed. If it was your son or relative you might refuse to press charges especially if they returned the money. They would have no case without that person testimony or if he refuse to press charges. .Defendant does not have to testify. So no prosecution. Doing the right thing can be rewarding. Something Trump is unfamiliar with is doing the right thing.
He stole the money but returned it. He stole the money and kept it. They are two different scenarios that would require different resolution.
The court can show mercy if there is reasonable cause. It is the judges discretion and prosecution discretion
Still returning the document shows character. Refusing to return the document when given multiple changes shows a lack of character and fear of admitting you made a mistake. Thus your in the denial mode and never will admit your wrong. Trump was given multiple chances to correct the problem. He refused. This is on him.
Bottom line, if Trump returned the documents when asked, then they would not press charges. They would respect him as the previous president.
That is why Trump case different from Biden's case. One showed a lack of character and willingness to deny that he made a mistake. While the other turned over the documents and accepted whatever fate had to offer.
Two tier system , it is a system that takes into account different scenarios and one shoes does not fit everyone.