Robeson was actually supposed to play 'Joe' in the original Broadway production, but a scheduling problem didn't allow it. However, he did appear in the run later, and then in three subsequent productions, including the London West End premiere.
I love Show Boat, to the point of awe. I've seen it on stage three times, and have several cast recordings. Not to mention numerous viewings of the two movie adaptations. That it was written about such powerful, controversial themes is one thing, rare for musicals, even today -- but that it was done in 1927, a time when shows were just a small step past vaudeville about light, frothy subjects, and Show Boat dealt with race, miscegenation, divorce and alcoholism is otherworldly remarkable. And remarkable too is that 1927 was a time when musicals didn't have songs integrated into the plot -- something that was still so uncommon 16 years later when Hammerstein teamed with Richard Rodgers for Oklahoma! that that show was seen as revolutionary. And now consider how many standards came from the show, some which are still even heard on occasion today. It's hard to name many songs from any shows in 1927 that became standards, let alone are still played, but Show Boat had songs such as "Ol' Man River," "Make Believe," "Can't Help Lovin' Dat Man," "Why Do I Love You?"," "Bill," and "You Are Love" (not to mention "Life Upon the Wicked Stage," and half a dozen other gems.) Then add that it was a mixed-race production in 1927.
And at the heart of it all is "Ol' Man River," the theme that runs through the show. Arguably it's the best song ever written for Broadway. (It would probably get my vote.) And it's reaches that stature because the song stands on its own for the strength of the music even without the lyrics, and the words without the music.
(Side note: there's a famous story, perhaps apocryphal, though who knows? Apparently, at a party, someone remarked to the wife of Jerome Kern how much she loved her husband's song, "Ol' Man River." As the story goes, the wife of Oscar Hammerstein II was there as well, and said, "No, Mr. Kern wrote, 'Dah dah dee dum.' My husband wrote 'Ol' Man River.'")
Much as I dearly love Show Boat, whenever there's a new production, and there raves about the actor playing 'Joe,' (usually well-deserved, I must note), I still hold it up against the standard. Not that the new performance isn't great on its own, but life is full of context. And saying that something is "great" is one thing -- but "great" compared to what, that is something else.
"Compared to this" is the standard. Some, as I said, do a wonderful job. But singing is more than having a good voice, or even a great voice. If you're going to sing "Ol' Man River," you'd better bring power, tenderness, sadness, hope and humanity.
Here's Paul Robeson. Even with the conventions of filmmaking and music arrangements and performance 78 years in the past, this is the standard.