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

Optimization · Pure Optimization
Tactical grid combat plus studio management, both solvable with planning.

Optimization · Pure Optimization
A vault management sim about optimising dwellers, rooms, and resource loops.
Chroma Squad leans Optimization (Pure Optimization); Fallout Shelter leans Optimization (Pure Optimization).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Chroma Squad
Turn-based commands, no dexterity involved
Fallout Shelter
Tapping menus only
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Chroma Squad
Enemy AI follows simple mappable rules
Fallout Shelter
No opponent
Fallout Shelter leans a little harder on variance, though the gap is small.
Chroma Squad
Hit rolls and episode events add modest noise
Fallout Shelter
Incident spawns and lunchbox loot rolls
Chroma Squad leans a little harder on optimization, though the gap is small.
Chroma Squad
Studio economy, crafting and teamwork combos are the puzzle
Fallout Shelter
Dweller stats and room layout are fully 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.