As I understand the law, the laws regarding possession of classified material require intent, so far, you could make the case that neither Biden or Trump intended to take classified data though there is reporting that Trump planned to take his. Where there is a distinction is obstruction of justice which Trump seems clearly guilty of and not Biden, thus far. If Biden has committed crimes he should be punished, same for Trump, who also may be charged with 1/6 related crimes as well. Yes you can punish one without punishing the other. They aren't the same thing.