I could see Sam Cooke being above Marvin Gaye, but it'd help the editors here (Zach and Nick) if you gave them more meat about your objection, applying it to the criteria, than just simply saying you question the artist's placements.
Negative Creep wrote:
He played a CRUCIAL role in the transition of r&b to 'soul'
As have others before him, including Ray Charles, The Dominoes, Johnny Ace, James Brown, Faye Adams, and The "5" Royales to name a few.
especially within the context of the gospel-flavored vocals.
James Brown and Ray Charles, again.
It's impossible to describe Sam's significance to his art.
It's not impossible to describe.
Gaye had more commercial success, but that's really the only immediate advantage I see.
You have to consider that Gaye was a monster of Motown, a major influence of the British Invasion and the development of rock and R&B/soul in particular, and has some of the most impacting, influential and beloved classic records of all time. That's just the surface. He's a major contender.
Anyway, I don't really have much to quibble about the artists in the Top 10.