head to head
Neither is meaningfully harder - they pose close to the same test. The widest gap is reads, and it is a single point.

Execution · Pure Mechanics
WWII gunfight execution with light multiplayer prediction.

Execution · Competitive PvP
Family-friendly class shooter pitting plants against zombies across PvP and co-op.
Call of Duty 3 leans Execution (Pure Mechanics); Plants vs. Zombies: Garden Warfare 2 leans Execution (Competitive PvP).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Call of Duty 3
Aimbot trivialises both campaign and multiplayer gunfights
Plants vs. Zombies: Garden Warfare 2
Third-person shooting with forgiving hitboxes
Plants vs. Zombies: Garden Warfare 2 leans a little harder on reads, though the gap is small.
Call of Duty 3
Multiplayer adds modest human positional prediction
Plants vs. Zombies: Garden Warfare 2
Human opponents adapt in PvP modes
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Call of Duty 3
Scripted setpieces and spawn flow add minor unknowns
Plants vs. Zombies: Garden Warfare 2
Class ability rolls are minimal
Plants vs. Zombies: Garden Warfare 2 leans a little harder on optimization, though the gap is small.
Call of Duty 3
Map knowledge and weapon choice reward light study
Plants vs. Zombies: Garden Warfare 2
Class counters and map knowledge help
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.