head to head
Neither is meaningfully harder - they pose close to the same test. The widest gap is optimization, and it is a single point.

Execution · Practiced Mastery
C64 classic about somersaulting past robots to assemble a password.

Execution · Twitch Chaos
Flipper execution and table knowledge with Pokémon-catching RNG on top.
Impossible Mission leans Execution (Practiced Mastery); Pokémon Pinball leans Execution (Twitch Chaos).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Impossible Mission
Pixel-precise flips past patrolling robots
Pokémon Pinball
Flipper timing and nudge control are the whole input
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Impossible Mission
Robots patrol on fixed behaviours
Pokémon Pinball
A pinball table has no mind
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Impossible Mission
Puzzle pieces randomized each playthrough
Pokémon Pinball
Ball physics and catch-mode rolls add real randomness
Impossible Mission leans a little harder on optimization, though the gap is small.
Impossible Mission
Search routing under the time limit
Pokémon Pinball
Mode routing and table knowledge raise scores predictably
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.