I think that even considering the times he was decked, it's ridiculous to question Gene Fullmer's chin.
Lausse was a massive puncher comparable to the biggest punches at that weight. I'd but Fullmer's chin on the same level as Eubank and Dick Tiger just below LaMotta at this weight. No doubt Gene has a quality chin and Ray stopping him with a single shot might be the greatest knockout ever largely due to Gene's proven durability. Ray couldn't seem to hurt him bad in any of their other meetings.
I'd probably put it on the same level as Ali and certainly higher then Oscar's who didn't fight nearly as many punchers and went down from Whitaker.
Minotauro. You can't put Gene's chin at Ali's level. Ali was never KO'd. Gene was KO'd by one punch to a 36 year old past prime Robinson, things like that never happened to Ali at Heavyweight and he fought massive punchers.
Plus Dick Tiger had a better chin than Fullmer. He was only KO'd by one shot by murderous Light-Heavyweight Bob Foster at age 37. He was never Ko'd before.
This is the first time I've ever heard anyone claim OSCAR DE LA HOYA(!!!!) had a better chin than Gene Fullmer.
What? De La Hoya fought bigger punchers than Fullmer. Trinidad, Pac, Mosely, Chavez, Mayorga, Vargas, and Gatti. And was never knocked out by any of them. De La Hoya's chin was amazing. Even when servely weight drained and weakend, Pac still cound't put him down or KO him.....
Pac and Gatti were far smaller and Chavez was shot. Trinidad and Mosley were big hitters Vargas was on the decline and Mayorga was never anything special. None of those guys beside maybe Tito had raw power like Fernandez or Lausse. Plus style wise Gener took more clean shots then Oscar who barley took a power shot from Felix, that's not Oscar fault of course but when assessing chins its something to look at. To the above poster while Ali never got KO'd he did get dropped by the likes of Cooper who wasn't a big puncher in comparison to some of the guys Gene fought p4p. Plus Ali never fought a puncher like Ray sure guys like Shavers, Foreman and co might have had the power but not the skill to land such a perfect shot. I think his chin is comparable to Ali and Tiger not to say better just around that level.
Robinson, Lausse, Fernandez, Tiger, Boyd, Webb, Basilio, and Turner hit as harder or harder than all those names you listed.
Fullmer had a VERY good chin. He was fighting the best in the world over and over again. So he got starched once by a perfectly timed shot by RAY ROBINSON for goodness sakes. But the other fights with Ray he was in his face for 15 rounds and not close to going down.