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
Comic-panel beat 'em up notorious for punishing health drain and tough fights.

Execution · Pure Mechanics
Punishing beat-em-up execution with zero margin and memorised stages.
Comix Zone leans Execution (Pure Mechanics); Double Dragon III: The Sacred Stones leans Execution (Pure Mechanics).
Comix Zone leans a little harder on execution, though the gap is small.
Comix Zone
Brutal one-life brawling demands clean play
Double Dragon III: The Sacred Stones
Brutal difficulty and no continues punish every missed input
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Comix Zone
Enemies follow fixed attack scripts
Double Dragon III: The Sacred Stones
Enemies attack in fixed scripted patterns
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Comix Zone
Everything is placed and scripted
Double Dragon III: The Sacred Stones
Stages never change between attempts
Comix Zone leans a little harder on optimization, though the gap is small.
Comix Zone
Panel routes and item use are memorizable
Double Dragon III: The Sacred Stones
Character-swap management and memorised layouts are the path through
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.