In his late thirties he lost to Pender twice, lost to Basilio, and went 1-2-1 with Gene Fullmer. We can extrapolate that he was very good in his prime, but the Bull still clearly defeated him, so "unbeatable" - no.
The bull is a top 30 ATG. And he outweighed Robinson by 16 pounds. I know Robinson is extremely beatable, at 160 that is.
In general. He's thought of very highly. But if you disagree that really isn't the point. The point is yes Robinson was defeated by Lamotta once. But he was a significantly bigger man. And could never make 147.
I get your point, but you have to be fair. The bull outweighted him by 16 pounds (today boxers make a drama for 2 pounds), he couldnt stand such a difference of weight. Edit: and beat the hell out of the bull the rest of his life.