The anti-circumvention list only blocks ads that EasyList cannot block. It does that by using experimental features
which allow Adblock Plus to fight against adblocker detection, adblocker circumvention, ad reinsertion and other malicious techniques that advertisers and publishers use to force ads onto adblocker users. Its smaller size when compared to EasyList also allows us to download it more frequently. Therefore it's not a replacement for EasyList but an enhancement to what EasyList can already block on its own.
It's also worth mentioning that other adblockers have similar lists which make use of their own experimental functionality.
Similarly, we are the ones maintaining the filter list so that we can swiftly respond to changes in anti-adblock scripts/techniques and to continuously improve the functionality while it's still experimental. That being said, it's open source and we are happy about contributions to the GitHub project.