That's not true.

A-ads is transparent, you can see the stats of any ad unit. Just find them with search or in the catalog. E g. this ad unit has just a few impressions a day and still earns (perhaps more than it should). Earnings depend on many factors, not only the traffic volumes (that can be faked).

It may take some time though for the ad unit to get moved to the appropriate categories by moderators and to start earning at full pace (if it doesn't happen in a few days - just let me know, I will try to help).