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 · Pure Mechanics
A bullet-hell shmup testing reflex dodging of scripted enemy patterns.

Execution · Practiced Mastery
Arthur's infamous SNES gauntlet of armor-shattering hazards that must be beaten twice with the right weapon.
Raiden IV OverKill leans Execution (Pure Mechanics); Super Ghouls 'n Ghosts leans Execution (Practiced Mastery).
Raiden IV OverKill leans a little harder on execution, though the gap is small.
Raiden IV OverKill
Dodging dense bullet patterns demands precise reflexes
Super Ghouls 'n Ghosts
Committed double jump and relentless hazards punish errors
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Raiden IV OverKill
Enemies fire fixed scripted patterns, not adapting
Super Ghouls 'n Ghosts
Scripted spawns, no adaptation
Raiden IV OverKill leans a little harder on variance, though the gap is small.
Raiden IV OverKill
Some spawn and item randomness, mostly mappable
Super Ghouls 'n Ghosts
Chest contents and zombie spawns add light randomness
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Raiden IV OverKill
Memorizing patterns and scoring routes maximizes runs
Super Ghouls 'n Ghosts
Weapon management and mandatory second loop demand routing
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.