On Strips: Dateline: Danger!
Except you have to include several asterisks with that distinction.
"Mainstream" is one key, of course, since Jackie Ormes famously had worked on her various Torchy Brown comics going back as far as 1937, and Jay Jackson came along with Speed Jaxon in the 1940s.
"Comic strips" is also noteworthy since Lobo headlined his own comic book title back in 1965, after All-Negro Comics debuted in 1947.
Even so, I find "lead" questionable as well. Morrie Turner began Wee Pals in 1965 and, though it featured a large regular cast, Nipper (who was based on Turner himself) was undoubtedly a, if not the, central figure from the very start of the strip. In fact, Nipper's Civil War kepi was a central gag in some of the earliest strips. I'm not sure how that doesn't qualify as "co-lead."
I'm not dismissing Dateline: Danger! as receiving unwarranted attention -- I'm betting you've never even heard of it, so it couldn't be getting that much attention -- but I think it's definitely more of a second-man-to-walk-on-the-moon-on-a-Tuesday kind of thing. Saunders and McWilliams were heavily borrowing themes from an existing television show -- a popular one, at that -- and were following behind any number of other comics creators who'd already pushed racial boundaries in comics. Both creators were Caucasian, as well, so even later strips like Quincy and Luther were more significant for having Black creators and having the strips titled after Black characters.
Still, comic strip history is worth studying for its own sake, so it's worth taking a look at Dateline: Danger! But it's also worth keeping some historical perspective when looking at it.