head to head
Neither is simply harder - they are hard in different places. Anthem demands more variance; Grand Theft Auto V demands more reads.

Optimization · Practiced Mastery
A co-op looter shooter about flying exosuit javelins through a hostile alien frontier.

Execution · Practiced Mastery
Sandbox crime playground spanning shooting, driving, and a persistent online economy.
Anthem leans Optimization (Practiced Mastery); Grand Theft Auto V leans Execution (Practiced Mastery).
Grand Theft Auto V leans a little harder on execution, though the gap is small.
Anthem
Flight and shooting matter but are forgiving
Grand Theft Auto V
Driving and shooting demand decent inputs.
Grand Theft Auto V leans clearly harder on reads.
Anthem
Enemy AI is scripted
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Anthem leans clearly harder on variance.
Anthem
Loot rolls gate power
Grand Theft Auto V
Some mission and lobby randomness.
Anthem leans clearly harder on optimization.
Anthem
Javelin builds and loadout grinding dominate
Grand Theft Auto V
Heists, money loops, builds learnable.
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.