I have recommended that people read David Olusoga and do so again.
If mention has been made of the Greeks, when someone raises the question of the Elgin Marbles it is difficult to aviod them.
Whataboutery is accusing the initial accuser of hypocrisy without addressing their point. In this case, the initial point that "The English started the slave trade. They caused all our problems.." is as historically inaccurate as it is geographically illiterate.
Even if we correct it, like a primary school teacher, to "The British," we still have that definite article. The British, at that time, in the main, were poor and powerless. They took no part in the slave trade, did not benefit from it directly and would have been better off indirectly if it had never happened.
Saying I need to apologise for something my great great great great great great great grandad did is pretty mad. Saying I need to atone for what someone else's ancestor did because I am the same nationality as them is totally unhinged.
I am a kid from a Brixton council estate. I grew up with friends from all corners of the world. At secondary school my best friend was the son of a minister from Botswana active in supporting South African Exiles. I supported the Anti-Aprtheid Movement and got my ANC badge from the head of the ANC in London. I have met and sat at the feet of one of Joe Slovo's girls embarrassing her with my admiration. You call me a racist and I will smack you in the mouth.
What we do not need are binary baby narratives. It's complictaed. The problem is complicated and so the solution will not be simple. We are not America, luckily. We have our own unique history and our problems are our responsibility to solve. If we look to the examples of Northern Ireland (precarious) and South Africa (mixed) we can see that the first step is to acknowledge that the war is over and now we must build the peace together.
The wrongs of the past are in the past, but scars remain and they hurt. We must acknowledge the wrongs of today. We are a nation of massive inequality in which inequality of opportunity has been increasing. Some would call the presence of a black Old Etonian who went to Trinity and Harvard in the govt progress. Others would call it co-option that makes the problem worse.