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
The Genesis Castlevania tours war-torn Europe with whip-wielding John Morris and spear-vaulting Eric Lecarde.

Execution · Practiced Mastery
A handheld run-and-gun testing dodge precision and spawn memorisation.
Castlevania: Bloodlines leans Execution (Practiced Mastery); Metal Slug Advance 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.
Castlevania: Bloodlines
Stiff classic movement against demanding Genesis bosses
Metal Slug Advance
Dodging dense fire with one life bar demands precision
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Castlevania: Bloodlines
Scripted monsters throughout
Metal Slug Advance
Enemy soldiers spawn on strict scripts
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Castlevania: Bloodlines
Minor hidden items only
Metal Slug Advance
Card drops add light collection randomness
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Castlevania: Bloodlines
Character choice changes paths; patterns are learnable
Metal Slug Advance
Memorising spawns and card abilities optimises every mission
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.