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.

Execution · Competitive PvP
Large-scale modern combined-arms shooter built on destructible maps and squad teamwork.

Execution · Practiced Mastery
A team shooter where aim and positioning against human opponents controls the map.
Battlefield 3 leans Execution (Competitive PvP); Splatoon 2 leans Execution (Practiced Mastery).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Battlefield 3
Gunplay, suppression management, and vehicle piloting
Splatoon 2
aim and movement decide ink battles
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Battlefield 3
Human teams adapt routes and armor pushes
Splatoon 2
predicting human opponent positioning
Battlefield 3 leans a little harder on variance, though the gap is small.
Battlefield 3
Spawns, destruction, and vehicle drops shuffle engagements
Splatoon 2
weapon and map rotation randomness
Splatoon 2 leans a little harder on optimization, though the gap is small.
Battlefield 3
Unlock paths, class synergy, and map control
Splatoon 2
loadout and turf strategy 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.