head to head
Grand Theft Auto V asks more than Alien Breed: Impact, and the gap is reads.

Execution · Practiced Mastery
Steady aim against scripted alien swarms with an upgrade economy underneath.

Execution · Practiced Mastery
Sandbox crime playground spanning shooting, driving, and a persistent online economy.
Alien Breed: Impact leans Execution (Practiced Mastery); Grand Theft Auto V leans Execution (Practiced Mastery).
Alien Breed: Impact leans a little harder on execution, though the gap is small.
Alien Breed: Impact
Kiting alien swarms top-down demands steady aim and movement
Grand Theft Auto V
Driving and shooting demand decent inputs.
Grand Theft Auto V leans clearly harder on reads.
Alien Breed: Impact
Aliens swarm on scripts, never modelling you
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Alien Breed: Impact
Ambush triggers are scripted-but-unknown first time through
Grand Theft Auto V
Some mission and lobby randomness.
Alien Breed: Impact leans a little harder on optimization, though the gap is small.
Alien Breed: Impact
Weapon upgrades and ammo economy reward planning
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.