Linares has often been said to have a weak chin, and indeed, all 4 of his losses were by stoppage, but I don't know if it necessarily means he has a weak chin. It's not like he's been knocked out cold. He's been knocked down quite a few times, but he's gotten back up more often than not. I think it's more because his defense is bad, combined with cutting easily.
His defense isn't bad either the only time he's been legit KO'd was against Salgado, who was a big puncher, and that was years ago and he got caught with one of those Boone or Edwards like bombs he didn't see coming. It happens. He wasn't even knocked down against DeMarco, he was wilting due to loss of blood, and the KD against Thompson was due to Linares being and looking overwhelmed after Sergio landed a bomb that opened up a cut, for good reason, Sergio flurried like a madman landing several flush shots, Jorge was more discombobulated than anything. His chin while not titanium, its fine.
This. Linares has quick hands and is a good boxer, but he always has and always will come up short against top competition due to his lack of power and durability.
Not awful defense but could be better for a guy with his technique and athleticism, I'd definitely say it's one of his weak areas.
And often weirdly enough you'll see him just slip punches through that are kinda odd. Like he'll just randomly get hit with a lead right hand out of nowhere with no setup, basically one of those guys who seems to switch off defensively at times.