Regarding the Robinson-Abrams bout, here's what Sid Feder reported. "The Harlem stringbean lost two of the 10 rounds on fouls. Actually he tossed 10 pitches out of bounds. Abrams won everything but the decision and large number of the 15,064 customers, who chipped in to a gross gate of $80,772, indicated disapproval of the verdict. The Associated Press score card gave it to Abrams, six rounds to three, with one even." That's 10 low blows by this account. Brilliant as Robinson was there is no doubt he used illegal blows to get the advantage. A good example is when he hammered Turpin's kidneys in the rematch to straighten him up for the finish. That should be punished. Judge Marty Munroe also went for Abrams, 6-4, hence arguably beaten, and yes, that is a big deal when weighing the careers of Cerdan and Thil.
No, you're right, many preferred Cerdan as a welterweight so there's lots of variables here. Career wise it is close. In terms of visual evidence I'm more impressed by Cerdan's textbook pressure.