head to head
Neither is simply harder - they are hard in different places. Grand Theft Auto V demands more reads; X-Morph: Defense demands more optimization.

Execution · Practiced Mastery
Sandbox crime playground spanning shooting, driving, and a persistent online economy.

Optimization · Practiced Mastery
A hybrid testing maze-planning optimization backed by twitch shooting between waves.
Grand Theft Auto V leans Execution (Practiced Mastery); X-Morph: Defense leans Optimization (Practiced Mastery).
X-Morph: Defense leans a little harder on execution, though the gap is small.
Grand Theft Auto V
Driving and shooting demand decent inputs.
X-Morph: Defense
Piloting the fighter through waves demands twitch dodging and aim
Grand Theft Auto V leans clearly harder on reads.
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
X-Morph: Defense
Enemy waves are scripted - nothing adapts to your maze
Grand Theft Auto V leans a little harder on variance, though the gap is small.
Grand Theft Auto V
Some mission and lobby randomness.
X-Morph: Defense
Wave compositions are known and repeatable per level
X-Morph: Defense leans clearly harder on optimization.
Grand Theft Auto V
Heists, money loops, builds learnable.
X-Morph: Defense
Tower placement and maze routing decide whether waves break
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.