congress can impeach him, which makes those pardons null

Biden didn't pardon himself afaik.

But... that's still perfectly legal, isn't it? All of these little backdoors the founding fathers added to the executive as some vestigial organ of monarchical power just because they couldn't trust the people in "we the people" maybe should be reconsidered. If we don't want presidents to be able to pardon themselves and anyone else without limit, there are ways to make that happen. Never even bothering to convict any president of a crime doesn't even attempt to fix that problem however.