Problem is a lot of black/minority characters were created to fulfill minority quotas rather than as legitimate characters, and since the writers largely aren't black and they see themselves as writing for a mainly white audience they don't care to put the work in, and sometimes when they do you end up with Rudyard Kipling-esque stereotypes infecting the characters/plot.
And since the most iconic characters in comics were created in an era where white was the only acceptable default, it's harder for black characters (especially when tons of them were created as sidekicks or as people to mirror other already successful comic characters) to break through that barrier.
This is why I generally don't have a problem with changing the race of comic characters like Peter Parker or Johnny Storm, when it's really irrelevant to the characters most of the time and they're always rebooted, it could do a lot to help children.
Anyways if you actually read comics you'll probably find a ton of great black characters.
First of all Black Panther is the GOAT all time superhero. He doesn't talk like an alien I don't know where the hell you got that notion.
When written well (Hudlin, Priest) Black Panther is truly unfukkwittable.
Static Shock is also an underrated superhero.
John Stewart is definitely God Tier but his potential for rich storytelling and overall swag and excellence doesn't match T'Challa
Eh, there's enough people on par with Black Panther imo, he's just the largest male black non John hero (though the movie may have put him above John I dunno).
Anyways, where are you getting this idea that John Stewart is God Tier?
If we're talking animated Stewart you have a point, but DC has some race issues and has tried their hardest to push him away/not give him significant roles or develop on the interesting parts of his character/backstory, hell they canceled Mosaic even though it was selling really well and could have done a lot for his character.
There's not much you can say about Stewart aside from that he's a strong, stern black man who's the first human to become a Green Lantern, that's an architect (which they could use a lot more for his character aside from his weapon designs).
Occasionally they'll do something nice like the willpower page, but it's not enough, hell a lot of the strongest advocates for black characters in comics/Black Panther don't even give him that high of praise, and generally his biggest fans still argue that DC needs to do a lot more for him.
Which is sad because DC had an entire generation of people including myself who thought that the definitive Green Lantern WAS black (with most people only finding out through the movie), and instead of capitalizing on it, they decided to double down on their golden boy Hal Jordan despite many people from every race wanting to see Stewart more, luckily with the shift in DC comics recently we should be seeing John get a lot more material
And maybe improvements in Cyborg beyond being randomly given significant focus, he seems to only be good in Teen Titans.