Without knowing the nature of the documents recovered from Biden there's no way to tell just how sensitive the information was. There's a world of difference between a secret memo from 2009 about re-allocation of replacement parts to a warehouse in Germany VS. a document outlining nuclear protocols and practices on an active submarine (as examples). Some things labeled "Secret" or "Top Secret" really are inconsequential whereas others are far more dangerous (like all that SCI information recovered from Trumpland)
The difference as I see it is that one of these Presidents found something in their house and proceeded to turn it over while conducting a search for anything else that shouldn't be there while the other one of these "Presidents" kept something in their house they clearly should not have had and then gave the authorities the runaround when they came to collect it.
In either case, it's pretty obvious that sensitive document tracking needs to be improved, but beyond that there doesn't seem to be much similarity between the circumstances.