Mouse studies with 1 percent linoleic acid vs. 8 percent show protection vs. weight gain, the difference between the supposedly fattening effects of a high fat diet for mice disappears when you correct for this. This looks on the order of the linoleic acid difference shown in this study in the coconut oil vs. coconut oil plus soy oil groups. A little fish oil also protects.
I remember Stephan Guyunet used to put the upper level for linoleic acid on a paleo type diet at about 4 percent, though I don't know whether he based this on controlled studies or more traditional levels of intake.
The fattening effect has sort of been traced down to endocannabinoid production, the linoleic acid is made into arachiconic acid which is used to produce endocannabinoids. The proof is that blocking endocannabinoids will reverse the fattening effects--but maybe not that surprisingly, in humans, endocannabinoid blockers are problematic in that they cause depression. And one symptom of depression is a decrease in appetite. So you gotta be a bit careful with this stuff. Omega 6 fatty acids aren't like cigarettes, just essential fatty acids that it might be possible to have too much of. Even that's uncertain. The !Kung people, I believe they're the folk in the Gods Must Be Crazy, traditionally eat as much as 60 percent of their diet from a nut that's a rich source of linoleic acid. Acorns are another rich source, even when our ancestors didn't eat them, their food did.
I'm not saying, this paleo group eats/ate it, so it must be safe for everybody, just pointing out that the evidence vs. omega 6 isn't perfect. I think it's prudent to keep it lowish but not absent--but sometimes things get a bit inflated, overestimate the importance of one factor, and there's a danger that some other more significant factor might seem less important by contrast.