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

Execution · Practiced Mastery
The sequel adding Horde mode to the campaign-plus-versus cover shooter formula.

Execution · Competitive PvP
Family-friendly class shooter pitting plants against zombies across PvP and co-op.
Gears of War 2 leans Execution (Practiced Mastery); Plants vs. Zombies: Garden Warfare 2 leans Execution (Competitive PvP).
Gears of War 2 leans a little harder on execution, though the gap is small.
Gears of War 2
Gnasher battles and movement tech set the ceiling
Plants vs. Zombies: Garden Warfare 2
Third-person shooting with forgiving hitboxes
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Gears of War 2
Human opponents in versus drive prediction play
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.
Gears of War 2
Horde spawns add mild randomness
Plants vs. Zombies: Garden Warfare 2
Class ability rolls are minimal
Gears of War 2 leans a little harder on optimization, though the gap is small.
Gears of War 2
Power-weapon timing and positioning are solvable
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.