I would suggest going to CPA or PPD in low volume traffic. A knowledgeable marketer know how to incorporate the right monetization. Do not force one way of monetizing things, test it, understand it.
Know your traffic, your audience, your layout and their behavior.
Let me give you an example. I have tons of websites and some of them run on adsense, some on CPM, some on PPI, Some on amazon, and some on CPA.
When my site who is running in PPI is switch to PPD/CPA it has a lower earning monthly than when it is in PPI. I would not go to details but it seems that every install gives me around .05-.06, when in PPD/CPA it gives me around .50-.70 oer download on average. It may seem that the PPI should have lower monthly income than in PPD/CPA but the problem lies in conversion. in every 50,000 UV in PPD/CPA it only gives me around 1%-2% conversion rate. While in PPI it gives me around 50-60% conversion rate on the same UV. (Notice I said UV, not clicks since clicks will not really give you the correct value of things).
Now you can say that I have shitty traffic and I need to get more quality traffic. Well in my point of view, I have just the right traffic for PPI it converts well for me, So why should I change it. If I want to use PPD then I will create a brand new campaign that will suit that monetization.
In the end I get tons of money from testing things out and choosing the optimal value of things.
TL;DR = Stop complaining and test things out. PPI, PPD/CPA, CPC, Affiliate, CPM and any form of monetization needs testing. You are the marketer it is your job to test things out!