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 · Competitive PvP
Hardcore team shooter where one bullet kills and the HUD tells you nothing.

Execution · Pure Mechanics
A fast arena shooter where twitch aim and movement against human opponents is everything.
Insurgency leans Execution (Competitive PvP); Unreal Tournament 2003 leans Execution (Pure Mechanics).
Unreal Tournament 2003 leans a little harder on execution, though the gap is small.
Insurgency
One-shot lethality rewards precise aim
Unreal Tournament 2003
aim and movement speed decide duels
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Insurgency
Human squads flank and adapt each round
Unreal Tournament 2003
predicting human opponent positioning
Insurgency leans a little harder on variance, though the gap is small.
Insurgency
No killcam or HUD hides enemy positions
Unreal Tournament 2003
weapon and pickup spawns vary
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Insurgency
Loadout points and objective route knowledge
Unreal Tournament 2003
map control and item timing 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.