Whether or not trump has the ability to declassify anything he wants is irrelevant to the fact that the documents do not belong to him and instead belong to the National archives, a fact some people seem to want to completely ignore while they find sources that support their feels.
This is true, and so long as you are merely talking about whether or not Trump supporters should be outraged by Trump's activities, then this is spot on. Even if they can imagine him finding a legal defense that criminally excuses his conduct, there is no question he has acted in a way that should convince
all people to keep him as far away from government office as possible.
From a criminal prosecution standpoint, that these items were classified is still heavily relevant. Although the statutes referenced in the search do not state anything has to be classified, it would be breaking ground, and the classified nature of the documents was certainly highlighted in the affidavit for the search warrant.
All that said, the chance that Trump actually communicated an intent to declassify these documents to anyone is essentially null by his own admissions. A "standing order" to declassify documents removed from the oval office has dubious legality, not to mention no one has corroborated Trump's assertion that he ever made such an order. Regardless, none of the documents were actually
marked as declassified, so Trump has a huge uphill climb to face in proving that they were. It is also likely to be made irrelevant by the existence of documents which he does not have at will power to declassify.