head to head
Neither is simply harder - they are hard in different places. ARC Raiders demands more variance; StarCraft II: Wings of Liberty demands more optimization.

Execution · Grand Arena
An extraction shooter where scavengers dodge killer machines and rival squads for loot.

Execution · Grand Arena
Real-time strategy where hands, reads, and build optimization all matter at the top.
ARC Raiders leans Execution (Grand Arena); StarCraft II: Wings of Liberty leans Execution (Grand Arena).
StarCraft II: Wings of Liberty leans clearly harder on execution.
ARC Raiders
Gunplay and movement under machine fire
StarCraft II: Wings of Liberty
APM, macro, micro-control under pressure
StarCraft II: Wings of Liberty leans clearly harder on reads.
ARC Raiders
Rival squads ambush, bait, and adapt
StarCraft II: Wings of Liberty
1v1 ladder vs adaptive humans modeling you
ARC Raiders leans clearly harder on variance.
ARC Raiders
Loot spawns and unknown player positions
StarCraft II: Wings of Liberty
map spawns minor; mostly known
StarCraft II: Wings of Liberty leans clearly harder on optimization.
ARC Raiders
Loadout economy and map knowledge compound
StarCraft II: Wings of Liberty
build orders, economy curves heavily solved
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.