First off, Black Widow has not been released in China yet. So you cannot make an accurate comparison of the data when only
WW84 was released in China. That's bad math.
Second, China also has a notorious piracy problem. Streaming movies make it very easy to pirate them, that is why WB release's their movies globally a week before they release it in America, because HBO Max is only available in America and it was an attempted to curb some of the money loss due to piracy.
Black widow is also being effected by piracy ,
that was why the move had a 69% box office drop it's second week.
Which is coincidently very similar to WW84 box office drop of 67%.
Not to mention, it's cheaper to see
Black Widow in theaters since it's an extra $30 to purchase it on Disney +. While
WW84 was free to many depending on their service provider, or came at no extra charge to those with HBO Max and was
the most watched movie Christmas day.
The truth is, it is unfair to judge the success of both movies or any movie released during the pandemic because of piracy and in the case of WW84 especially, no vaccines being available to the public. Also, Black Widow is not released in China, so I don't know how you can make a comparisons when both movies where released under widely different circumstances.