head to head
Neither is meaningfully harder - they pose close to the same test. The widest gap is reads, and it is a single point.

Execution · Practiced Mastery
Combo execution and line routing through fixed skateparks for maximum score.

Execution · Practiced Mastery
A story-driven skateboarding game still won by trick execution.
Tony Hawk's Proving Ground leans Execution (Practiced Mastery); Tony Hawk's Underground 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.
Tony Hawk's Proving Ground
Perfect inputs chain manuals, grinds and Nail-the-Trick combos indefinitely
Tony Hawk's Underground
Combos plus off-board tricks keep the input ceiling high
Tony Hawk's Proving Ground leans a little harder on reads, though the gap is small.
Tony Hawk's Proving Ground
Multiplayer score battles barely involve predicting opponents
Tony Hawk's Underground
Story missions are scripted, not adaptive
Tony Hawk's Proving Ground leans a little harder on variance, though the gap is small.
Tony Hawk's Proving Ground
Skateparks are fixed and fully learnable
Tony Hawk's Underground
Fixed levels and mission scripts
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Tony Hawk's Proving Ground
Routing the highest-scoring combo line through terrain is the meta
Tony Hawk's Underground
Mission and score-line routing remain 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.