Arbitrage is what you buy at and what you sell at. CTR is not really of importance. Some of my most profitable campaigns have a shit ctr. High ctr with low follow up action is the worst thing you can have. Basically you are just paying for traffic that bounces or at best turns into cpm revenue!
If your just looking at monetizing on cpm you have to drive 10,000 people per day minimum just to make $100. If you can get them to take an action you can make a lot more.
The advantage of a funnel is I can effectively sell the same traffic over and over because if I can get them into my funnel I pay almost nothing to re-market to them. It is that backend where all the money is made. So the action i focus on is getting them in my funnel and monetising them afterwards.
The funnels are not porn, so it is irrelevant if the traffic is porn or not, I just buy whatever is the cheapest that day. Some days Google Adwords makes a better roi!
The key is that there is a value to each person in my funnel , so long as I am paying less than that to get them in it I make money. That is my business model.