head to head
Neither is harder. They score identically on all four axes, so the difference between them is in kind, not degree.

Optimization · Mind & Math
The original historical RTS of advancing ages, booming economies, and rushing armies.

Optimization · Mind & Math
A colonial-era RTS adding home-city card shipments to classic Age economy play.
Age of Empires leans Optimization (Mind & Math); Age of Empires III leans Optimization (Mind & Math).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Age of Empires
APM and micro under pressure
Age of Empires III
Unit micro and raid defense
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Age of Empires
Scouting and countering human strategies
Age of Empires III
Human deck and timing reads in ranked
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Age of Empires
Fog of war and map resources
Age of Empires III
Map spawns and shipment ordering unknowns
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Age of Empires
Build orders and eco timing dominate
Age of Empires III
Home-city decks are a build-crafting layer
A matching score does not mean a matching test. Two games can both sit at 10 on execution and demand completely different things of you - which is why the reasoning above matters more than the number beside it.