head to head
Neither is simply harder - they are hard in different places. Pong demands more reads; Wii Sports Resort demands more variance.

Execution · Competitive PvP
The original reflex duel - paddle precision with a thin layer of placement prediction.

Execution · Pure Mechanics
Island-themed collection of twelve motion-controlled sports showcasing the Wii MotionPlus accessory.
Pong leans Execution (Competitive PvP); Wii Sports Resort leans Execution (Pure Mechanics).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Pong
Paddle positioning and return angles are pure motor skill
Wii Sports Resort
MotionPlus precision in swordplay, archery and bowling
Pong leans clearly harder on reads.
Pong
Against a human, anticipating placement adds a thin prediction layer
Wii Sports Resort
Local versus duels involve mild feinting
Wii Sports Resort leans clearly harder on variance.
Pong
Fully deterministic ball physics
Wii Sports Resort
Slight physics and CPU pattern randomness
Wii Sports Resort leans clearly harder on optimization.
Pong
Angle strategy is shallow and quickly exhausted
Wii Sports Resort
Each event has small learnable technique optima
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.