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
A vault management sim about optimising dwellers, rooms, and resource loops.

Optimization · Pure Optimization
Type-matchup math and team construction across a scripted Sinnoh campaign.
Fallout Shelter leans Optimization (Pure Optimization); Pokémon Pearl Version leans Optimization (Pure Optimization).
Pokémon Pearl Version leans a little harder on execution, though the gap is small.
Fallout Shelter
Tapping menus only
Pokémon Pearl Version
Menu-driven battles need no dexterity
Pokémon Pearl Version leans a little harder on reads, though the gap is small.
Fallout Shelter
No opponent
Pokémon Pearl Version
Gym leaders are scripted; online battles are optional
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Fallout Shelter
Incident spawns and lunchbox loot rolls
Pokémon Pearl Version
Encounter tables and battle rolls are mappable RNG
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Fallout Shelter
Dweller stats and room layout are fully solvable
Pokémon Pearl Version
Team building and type matchups are the solvable core
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.