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 · Competitive PvP
Real-time arena aim duels against human worms with randomised weapon pickups.
Insurgency leans Execution (Competitive PvP); Worms Rumble leans Execution (Competitive PvP).
Insurgency leans a little harder on execution, though the gap is small.
Insurgency
One-shot lethality rewards precise aim
Worms Rumble
Real-time aim and movement decide brawls, unlike turn-based Worms
Insurgency leans a little harder on reads, though the gap is small.
Insurgency
Human squads flank and adapt each round
Worms Rumble
Human opponents in arena and royale modes can be predicted
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Insurgency
No killcam or HUD hides enemy positions
Worms Rumble
Weapon crate spawns and drop positions add randomness
Insurgency leans a little harder on optimization, though the gap is small.
Insurgency
Loadout points and objective route knowledge
Worms Rumble
Loadout knowledge and map control matter but stay shallow
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.