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
Momentum-driven execution over fixed levels rewarding memorised routes.
Castlevania: Bloodlines leans Execution (Practiced Mastery); Sonic the Hedgehog 3 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
Sonic the Hedgehog 3
Holding speed through fixed hazards demands sharp reactions
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
Sonic the Hedgehog 3
Badniks and bosses repeat identical 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
Sonic the Hedgehog 3
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.
Castlevania: Bloodlines
Character choice changes paths; patterns are learnable
Sonic the Hedgehog 3
Route choice and emerald collection reward memorised play
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.