head to head
Neither is harder. They score identically on all four axes, so the difference between them is in kind, not degree.

Execution · Pure Mechanics
Rhythm FPS where every shot must land on the metal soundtrack's beat.

Execution · Pure Mechanics
Memorising fixed spawn patterns and executing them flawlessly under one-hit death.
Metal: Hellsinger leans Execution (Pure Mechanics); Metal Slug XX 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.
Metal: Hellsinger
shooting on the beat is the entire skill test
Metal Slug XX
Dodging dense fire one-hit-death demands precise hands
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Metal: Hellsinger
demons follow fixed behavior
Metal Slug XX
Every enemy and boss is a fixed scripted pattern
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Metal: Hellsinger
deterministic arenas
Metal Slug XX
Levels never change between runs
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Metal: Hellsinger
weapon choice and streak management for scores
Metal Slug XX
Memorising spawns and weapon routes is the mastery path
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.