This is something you'd learn in your first year at law school. If, as Trump's complaint alleges, Dominion did destroy evidence then the evidence is immediately assumed to support the opposing party's allegations.
Biden's defense would now have to prove there was no fraud as if Trump's team had certain evidence of there being such.
What you're saying is: Biden has to prove something DID NOT happen.
Do you know how impossible it is to prove a negative? I'll give you a hint: in this particular case it's literally impossible.
It's really easy in this case, Biden (not literally Biden) has to prove that each ballot counted was a legal ballot. The evidence that can conclusively prove it is there, but they're destroying it.
It’s almost impossible to prove a negative in a real world setting. There’s an infinite amount of possible ways to cheat.
This is from a philosophy/math perspective. Proving a negative is notoriously impossible; good luck wasting your time.
It's not a negative, it's proving a positive. Htf can you have an election and not be able to prove the results?