The fact that black Nigerians are the most successful ethnic group in America is obviously an argument against the idea of systemic racism.
Two problems with your theory.
(1) "Black Nigerians" are not the most successful ethnic group in America. We have shown you that your one link doesn't even prove that they are, and we have shown multiple links that show they aren't. They are more successful than the average American. That's awesome. They are absolutely more education-centered than the average American, and their work ethic is superior to the average American. No argument from me on that. But they are not "the most successful ethnic group" in America. It simply is not a fact. You have stated it, but nothing you have provided supports it, and several sources in fact contradict it.
(2) If the definition of "systematic racism" was "a system in which all people of the un-favored races are denied opportunities 100% of the time, and all people of the favored races are given opportunities easily 100% of the time," then you would indeed be able to disprove its existence by pointing to Nigerian-Americans. Hell, you wouldn't even have to go that far. Just say, "Oprah Winfrey. One of the wealthiest women in the USA today, bar none. Game, set, match."
But that is not what "systematic racism" means.
Systematic racism means that the ***system*** -- not one specific person, not any group of people, but a system that has been put in place -- has made it so that it is actually harder for some people than for others. Not impossible for some and easy for others.
Here's a great example:
Imagine you're in a classroom. Traditional classroom, 4-5 rows of chairs, 4-5 kids in each row. The teacher places a waste basket at the front of the room and asks every student to crumple up a piece of paper and toss it in.
Most of the students in the front row are going to make the basket. Not all, but most. Especially the two kids in the middle.
There will probably be one or two kids in the back row who will manage to get a basket from way back there, but most probably won't. Especially the back two corners.
Obviously, there is a lot of skill involved in "making a basket." Kids who are good with gross motor skills and hand-eye coordination are going to do better. But no one is going to argue that the kids in the front row and the middle columns are at an advantage over the kids further away. Miles of "duh" at work here.
Systematic racism says that some people are closer to the "basket" than others, through no merit of their own, and some people are further away, through no fault of their own. It doesn't say people who are further away should just quit. On the contrary, a good teacher will encourage those two work all the harder.
Lots of groups work hard and respect education, but a group that happens to be black lands on top. Seems unlikely if the entire system is secretly conspiring against them.
Except it doesn't. In the US, the group on top is Korean Americans. Who are still victims of systematic racism, but since "systematic racism" doesn't mean "you'll never succeed" but rather "you have to work even harder to succeed," then the group(s) that push education and hard work the most are going to succeed the most.
Which means it makes total sense why Nigerans are above the median, and so far above native-born African Americans who are not born into the same culture of hard work and education.
The immediate rejection of Nigerian success in America by people that promote the idea of systemic racism makes it seem even more like a conspiracy theory.
I don't know who you think is "rejecting Nigerian success."
Myself and others are pointing out that Nigerian Americans are not, according to actual numbers, the #1 MOST successful demographic in the US. That isn't because we reject the success of Nigerians. It's because we reject false statements that are not based in facts and statistics from reputable sources like the US Census Bureau.
Someone who insists that "Nigerian Americans are the most successful group in America" despite being shown, multiple times, that this is simply not the case, according to the actual numbers, and insists that it is, repeatedly, seems to me like he'd rather cling to his own racism than accept reality.