From that link:

> However, the early design of GCL went for something simpler that coincidentally was also incompatible with the notion of graph unification. This simpler approach proved insufficient, but it was already too late to move to the earlier foreseen approach. Instead, an inheritance-based override model was adopted. Its complexity made the earlier foreseen tooling intractable and they never materialized. The same holds for the GCL offsprings that copied its model.

Needless to say I disagree with the Cue author. I think the inheritance-based override model is fantastic and has made for a great and straightforward configuration language.