An ADAS would be L4 if it was designed to be truly autonomous. If it's not designed to be truly autonomous, you have to somehow address the attention problem. Even a good attention monitoring system isn't sufficient, because people have the ability to appear superficially attentive by all external metrics, while not engaging with the driving task mentally.

The data to differentiate these levels is pretty limited for a variety of reasons, and the problem only worsens when you conflate AEB with ADAS as the IHS/IEEE do in this article rather than use an OEDR-based definition.