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
Arcade run-and-gun testing dodging execution and full memorisation of fixed spawn patterns.

Execution · Practiced Mastery
Combo execution layered over solving each park's optimal scoring line.
Metal Slug 2 leans Execution (Practiced Mastery); Tony Hawk's Underground 2 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.
Metal Slug 2
Bullet dodging and precise shooting under constant pressure
Tony Hawk's Underground 2
Combo timing, balance meters and manuals demand practiced hands
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Metal Slug 2
Every enemy and boss is a fixed arcade script
Tony Hawk's Underground 2
No opponent adapts; score attack is solo
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Metal Slug 2
Spawns are deterministic; nothing hidden after one credit
Tony Hawk's Underground 2
Maps and goals are fixed and fully knowable
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Metal Slug 2
One-credit clears come from memorising every spawn and pattern
Tony Hawk's Underground 2
Finding the highest-scoring line through each park is solvable
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.