Warcraft 3 also had a lot less interdependent moving parts. The 2.2 Stellaris AI has to manage food, minerals, energy, influence, unity and 3 different not interchangeable research resources as the basic empire wide stockpileable resources. It also has to cope with the more advanced resources, of which consumer goods and alloys are the simplest, have different purposes and are both manufactured from minerals and minerals alone, the advanced resources which can be made from minerals at great cost or mined directly, the planetary populations and relevant happiness factors, the planetary housing and amenity availability, the planetary stability and criminality scores, the soft empire size cap, the soft military unit cap, the soft starbase cap...
The list continues. Extensively. And that's just the resources involved, we're not even talking about unit design, fleet composition, diplomacy, expansion of the empire or a multitude of other factors.
Warcraft 3 only had gold and wood and a hard unit cap. Although Warcraft's combat mechanics are rather more involved than Stellaris', its economical factors are in comparison rather trivial in complexity and interaction.