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 · Practiced Mastery
A PvP-centric MMO where aerial execution and reading opponents in Abyss battles define competitive performance.

Execution · Competitive PvP
Combined-arms multiplayer shooter famous for map-altering levolution moments and 64-player conquest.
Aion leans Execution (Practiced Mastery); Battlefield 4 leans Execution (Competitive PvP).
Battlefield 4 leans a little harder on execution, though the gap is small.
Aion
Aerial combat and combo chaining require timing and positioning
Battlefield 4
Gunplay, vehicle mastery, and movement under fire
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Aion
Rifting and Abyss PvP feature real adaptive opponents
Battlefield 4
Human teams adapt to flanks and levolution chokes
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Aion
Enchantment stone RNG is a meaningful hidden-information layer
Battlefield 4
Map-altering events and spawns inject noise
Aion leans a little harder on optimization, though the gap is small.
Aion
Manastones and gear sets have well-known optimal configurations
Battlefield 4
Loadout tuning and objective rotation knowledge
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.