CTR is one piece. But conversion in another. And intent is important. Take two identical ads on Facebook and Google, with the same CTR and CPC, if the Google traffic has more intent to take action beyond the click (I'm not saying they are necessarily) then Google traffic is worth more. I worked in the LeadGen space for a good number of years and conversion rate is a very important piece of the puzzle. Generally speaking, intent leads to a better conversion. Plus, advertisers do them selves a disservice to attract higher clicks if that means their conversion rate is lower because the ad was bait. I've noticed that FB ads tend to have a spammy/scammy feel to them... bait.