You're not wrong.
Tombstone is ok. He's pretty much Max Cady from Cape Fear but with superpowers. Scary prison escapee with a grudge. If Marvel had better writers they could really do something with a psychotic killer who thinks he is some poor soul's ( Robbie Robertson) best buddy.
The joke is he's really Robbie's archfoe. Tombstone's way scarier for a normal person to have to deal with.
Centurius is a way obscure mad scientist type that was created by Jim Steranko in the 60's and literally disappeared until Thunderbolts started using him. But he's a more credible scientist type than Thunderball who let himself be bossed around by a cheap thug for decades.
I kinda think Black Manta got as far as he did because of how sad the rest of Aquaman's rogues were. And I think the editors themselves forgot he was Black. I don't remember ever seeing him without that helmet in the 70's in cartoons or comics.