While looking up some other bit of information about a Negro Leagues player, I saw a passing mention of John Donaldson, who a SABR researcher thought should be in the Baseball Hall of Fame in Cooperstown. I had never heard of Donaldson, which was a blow to my ego. I'm not an expert on black baseball, but I have read more than most, know the broad outlines, and should have at least heard of someone of that caliber.
The Pittsburgh Courier had a poll of players in 1952 of who were the greatest black players* of all time. I put a lot of stock in such things. Players can be biased in favor of guys they liked, and regional biases can push good players into greater prominence or obscurity than they deserve. At an individual level, players and fans can both be swayed by a few key moments in memory, when Oscar Charleston beat your hometown team three times in one season, or mighty Casey struck out. However, such things even out over large samples. Observation tells us one thing, statistics tell us another. By observation, players regarded him as a first-team starting pitcher. All the others are in the Hall of Fame: Smokey Joe Williams, Satchel Paige, Bullet Rogan, Bill Foster. Better-known pitchers Cannonball Dick Redding, Don Newcombe, Leon Day, and Luis Tiant Sr are on 2nd-5th teams. OTOH, Hilton Smith, who is in the Hall of Fame, isn't mentioned, so maybe the players don't always get it right.
Donaldson has statistics. 400 wins, 5,000 strikeouts, including an 18-inning, 31 strikeout game. Multiple no-hitters and one-hitters. While much of this was against inferior opposition as he was barnstorming in the Midwest, those are still very big numbers. He was almost a generation older than Satchel Paige and played in an era when major and minor leagues were more mixed. It isn't the same as baseball since 1940, when the best players moved automatically to MLB. The Pacific Coast League in the 1930's may have been the equal of the American and National Leagues - several PCL teams undoubtedly were. When Donaldson came into organised baseball in 1908, even the better-paid white players didn't make a lot, nor enjoy national reputations. The major leagues were known to have most but not all of the best teams. Good players were even more widely scattered. Professional baseball didn't pay so well that you'd want to drop everything and do that, leaving family and friends behind, so even some of the best players stayed home and played semi-pro.
John Donaldson toured with Satchel Paige's All-Stars in 1939 when he was 48. I'm thinking that in itself suggests how good he was. There is brief vimeo footage of him pitching.
*The Negro Leagues were only part of the story. There were about a half-dozen of those leagues beginning around 1920, most of them short-lived. Donaldson would have already been 29 by then. Black players mostly played on barnstorming teams that were part of no league until the 1930's, and by 1952 when the survey was taken a few had already made it to the majors.