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
Tests trajectory aim and turn planning against human targets amid crate luck.

Reads · Competitive PvP
Modern Worms with crafting and vehicles, keeping the classic turn-based destructible-terrain warfare.
Worms: Ultimate Mayhem leans Execution (Competitive PvP); Worms W.M.D leans Reads (Competitive PvP).
Worms: Ultimate Mayhem leans a little harder on execution, though the gap is small.
Worms: Ultimate Mayhem
3D grenade arcs and ninja-rope control reward practiced aim
Worms W.M.D
Shot arcs, rope swings and vehicle control demand precision
Worms W.M.D leans a little harder on reads, though the gap is small.
Worms: Ultimate Mayhem
Predicting a human's target priorities shapes each turn
Worms W.M.D
Multiplayer turns hinge on out-guessing rival worm placement
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Worms: Ultimate Mayhem
Crate drops, wind and terrain chaos swing rounds
Worms W.M.D
Wind, crates and random terrain reshape options
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Worms: Ultimate Mayhem
Weapon economy and positioning are plannable each turn
Worms W.M.D
Crafting and weapon budgeting reward planned turns
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.