Regarding Interest Based Ads:
In this scenario, we are assuming all bids and quality scores of said ads are the same.
If Google determines that the % chance of a click of said interest based user on an interest based placed ad is greater than the chance of a click on content placed ads, then the Interest-Based ad is placed.
Interest Based ads should make you more money in the long term. If they do not end up making more overtime, see above verbal algo.
Interest-Based ad bid = $5.00 with a 5% chance of being clicked
Content based ad bid = $2.00 with 10% chance of being clicked
Interest Based ad will be placed as it will make you (and Google) more money long term in this situation.
In summary, I do not feel Interest Based ads are responsible for a decline in anyone's earnings via Adsense.