Video game AI from 20 years ago was already good enough to perform ATC at an algorithmic level. It's not a difficult problem, if approached as a system, because there are no surprises left in the field. Every situation that will ever need to be handled by ATC has either been encountered and understood by now, or can reasonably be anticipated and modeled, making it a good candidate for automation.

The problem -- like self-driving cars that generally outperform humans but aren't allowed on the roads because occasionally they still screw up -- is primarily political, not technical. A rational point of view wouldn't demand perfect performances from machines that were never achieved by humans in the first place. Eventually lawmakers and regulators will get that through their heads, and we'll all be better off for it... but the transition will be a rough one.