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

Execution · Practiced Mastery
Cave's gothic horizontal bullet hell with player-chosen stage difficulty and item-chain scoring.

Execution · Practiced Mastery
Twitch dodging and shooting layered over memorised arcade stage routes.
Deathsmiles leans Execution (Practiced Mastery); Metal Slug leans Execution (Practiced Mastery).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Deathsmiles
Horizontal bullet dodging with dual-direction shooting
Metal Slug
Dodging dense bullet patterns and precise shots carry every credit
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Deathsmiles
Scripted gothic enemies never adapt
Metal Slug
Enemies follow fixed arcade scripts, never adapt
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Deathsmiles
Selectable difficulty fixes patterns, little randomness
Metal Slug
Spawns are nearly deterministic once a stage is learned
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Deathsmiles
Item counter and rank route choices drive scoring
Metal Slug
One-credit clears come from memorising routes and spawn patterns
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.