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.

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

Execution · Competitive PvP
Aim duels against human crews layered over hidden-information loot gambles and extraction timing.
ARC Raiders leans Execution (Grand Arena); Marathon leans Execution (Competitive PvP).
Marathon leans a little harder on execution, though the gap is small.
ARC Raiders
Gunplay and movement under machine fire
Marathon
Gunfights against other crews reward raw aim heavily
Marathon leans a little harder on reads, though the gap is small.
ARC Raiders
Rival squads ambush, bait, and adapt
Marathon
Predicting human crews' rotations and ambushes is constant
ARC Raiders leans a little harder on variance, though the gap is small.
ARC Raiders
Loot spawns and unknown player positions
Marathon
Loot spawns and unseen squads create hidden information
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
ARC Raiders
Loadout economy and map knowledge compound
Marathon
Loadout economics and extraction routing sit underneath
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.