I think you misunderstand how science works. Say the question to settle is whether black sheep exists or not.

Can you disprove their existence by showing me lots of white sheep? Of course not. You cannot prove a negative.

However to prove the existence of black sheep, all I need is a single sheep.

Systemic racism is like the black sheep. You only need to find some cases to prove it. Attempting to disprove it amounts to collecting a lot of white sheep and insist this proves black sheep do not exist.

You engage in a logical fallacy. A fairly large amount of studies show systemic racism. That is enough to prove it. That is eqivalent to finding numerous black sheep. That is more than enough evidence to prove the existence of systemic racism.

I would rather question, why you are so invested in the idea that it does not exist? Have you read American history. The history of systemic racism is quite long. There is nothing surprising about its existence. Quite the contrary it is more puzzling that people reject it. Which makes me ponder their ideological motivations.