I've run lead gen campaigns there that were almost comparable to Facebook but can't they "worked".

I think the problem is, as an advertiser, treating it like I do the other social channels. I don't feel like it's similar to Facebook at all and has become even more different over time. Pinterest has similarly fragmented.

I see using content as remarketing ads to be effective there. But that's the hardest ad-use-case to prove ROI on, in my experience.