I agree with that take, but this is an example of an “Oops I won’t do it again I promise” attitude in Washington DC politics in general. The “having documents you’re not supposed to” has happened with a lot of ex-officials, including Democrats, but it’s usually hand-waved away as long as they destroy/return them. I don’t think that is Biden trying to not appear partisan as much as it is Standard Operating Procedure with politicians, and they just didn’t expect an actual all-out criminal to refuse to give them back, like Trump.