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.

Optimization · Pure Optimization
Strategy sim about evolving a pathogen to outpace the world's cure effort.

Optimization · Pure Optimization
Lane defense classic about managing a sun economy against shambling waves.
Plague Inc. leans Optimization (Pure Optimization); Plants vs. Zombies leans Optimization (Pure Optimization).
Plants vs. Zombies leans a little harder on execution, though the gap is small.
Plague Inc.
Tapping menus only
Plants vs. Zombies
Clicking to plant, minimal pressure
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Plague Inc.
World response is algorithmic, not adaptive to you
Plants vs. Zombies
Zombie waves follow set compositions
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Plague Inc.
Spread events and cure pace fluctuate
Plants vs. Zombies
Wave timing and lane pressure vary mildly
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Plague Inc.
Evolution-point timing strategies are largely solved
Plants vs. Zombies
Sun economy and lane setups are near-solvable
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.