When I am using adplexity I still see many sites using adsense to monetize their pages so I assume arbitrage is still working for some people but it is likely very optimized. I assume it would take some serious work to get it working but pretty much everything takes hard work
One challenge will be to make sure you don't break adsense policies.
With few exceptions,most of those arbitrage sites belong to ad networks. They tend to use them for their unsold inventory.