head to head
Fallout: New Vegas asks more than Plants vs. Zombies, and the gap is execution.

Optimization · Pure Optimization
A faction-driven RPG-shooter where build and route planning shape every ending.

Optimization · Pure Optimization
Lane defense classic about managing a sun economy against shambling waves.
Fallout: New Vegas leans Optimization (Pure Optimization); Plants vs. Zombies leans Optimization (Pure Optimization).
Fallout: New Vegas leans clearly harder on execution.
Fallout: New Vegas
Shooter inputs with VATS assist
Plants vs. Zombies
Clicking to plant, minimal pressure
Fallout: New Vegas leans a little harder on reads, though the gap is small.
Fallout: New Vegas
Scripted factions and enemies
Plants vs. Zombies
Zombie waves follow set compositions
Plants vs. Zombies leans a little harder on variance, though the gap is small.
Fallout: New Vegas
Some loot and crit RNG
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.
Fallout: New Vegas
Faction routing, perks, builds heavily rewarded
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.