I don't agree with your point, but the interesting thing about this case is we don't have to agree about the exact status of the classified documents.
He was informed that he was in possession of government records and was asked to return them. He returned some of them without making any legal argument of any kind as to why was in rightful possession of the remaining records. The government came back again and ask for all of the records, and he again provided some, but not all, still offering no legal argument regarding continued retention and even pledged that he had provided all of the documents as requested. Then, only after an informant notified the government that FPOTUS was still in possession of documents and then secured a subpoena to go and get them, did these bogus lines of argument start to be offered in defense.
If Trump legitimately thought he was the rightful possessor of the documents, why didn't he make that argument during the eighteen months between when he left office and when the FBI/DOJ came the third time to finally collect all of the material?
And beyond any of that, I still have not heard anyone make a cogent argument as to what legitimate purpose FPOTUS had for the type of top secret documents we now know he was keeping in multiple places at a public country club. It staggers the mind to think that anyone still feels there is a defensible argument here, particularly those in the "but her emails" crowd who were chanting for Hills to be locked up.