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
Building a team and exploiting type-matchup math against scripted trainers.
Fallout Shelter leans Optimization (Pure Optimization); Pokémon LeafGreen Version leans Optimization (Pure Optimization).
Pokémon LeafGreen Version leans a little harder on execution, though the gap is small.
Fallout Shelter
Tapping menus only
Pokémon LeafGreen Version
Menu-driven turn battles demand no physical skill
Pokémon LeafGreen Version leans a little harder on reads, though the gap is small.
Fallout Shelter
No opponent
Pokémon LeafGreen Version
Trainers are scripted; link battles are a side mode
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 LeafGreen Version
Wild encounters, catch rolls and crits add 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 LeafGreen Version
Type matchups and team building 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.