My point is, stating "too many minority characters" don't sell books is as erroneous as saying "too many green characters" don't sell books. And just because you site an article that is 6 years old doesn't make your point any more valid. Your argument is flawed and your proof is based on opinion. Be it Spawn or Miles Morales, a minority character can and has carried a book, a well written book is a well written book, regardless of the skin color of it's characters.
I like to think that when your typical purchasing audience is older, male and middle class*, they want a good book over a book full of characters that look just like them. So to draw your conclusion just seems fallacious.
Now if you want to make an argument regarding poorly written or pointedly written books like Marvel's 'America' by Gabby Rivera, well, that is a different story. That book I can not defend for so many reasons. But that has to do with someone pushing their political view.
Any response on why the book doesn't sell well will be an opinion. But I would argue that my opinion is not baseless. The numbers and trends are my evidence. Miles Morales is profiting off of the Spider-Man name, which is the point of Marvel's much complained about racial and gender swapping of their popular characters.
Spawn is relatively probably the best selling black character of all time, but understand that Spawn is the pet character of the owner of Image and therefor was pushed. Ironically, I recall McFarlane himself making a controversial statement that Spawn sells well because his disfigurement hides his race. And Spawn sells relatively well. In other words, it sells well for an Image book, but in actual numbers is fairly low compared to Marvel and DC books.
And I agree that the current America book is horrible. I think she is a great character and I'm caught between the desire to see the character do well and my desire to see Rivera off of the book. I wouldn't mind if she pushed her political views as long as the writing and stories are of quality.