head to head
Neither is simply harder - they are hard in different places. Grand Theft Auto V demands more reads; Super Mario Bros.: The Lost Levels demands more execution.

Execution · Practiced Mastery
Sandbox crime playground spanning shooting, driving, and a persistent online economy.

Execution · Practiced Mastery
The famously punishing Japanese sequel to Super Mario Bros., built for players who mastered the original.
Grand Theft Auto V leans Execution (Practiced Mastery); Super Mario Bros.: The Lost Levels leans Execution (Practiced Mastery).
Super Mario Bros.: The Lost Levels leans clearly harder on execution.
Grand Theft Auto V
Driving and shooting demand decent inputs.
Super Mario Bros.: The Lost Levels
Brutal precision jumps, poison mushrooms punish any input slip
Grand Theft Auto V leans clearly harder on reads.
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Super Mario Bros.: The Lost Levels
No adaptive opponent; everything is scripted
Grand Theft Auto V leans a little harder on variance, though the gap is small.
Grand Theft Auto V
Some mission and lobby randomness.
Super Mario Bros.: The Lost Levels
Hidden blocks and warp zones until memorised
Super Mario Bros.: The Lost Levels leans clearly harder on optimization.
Grand Theft Auto V
Heists, money loops, builds learnable.
Super Mario Bros.: The Lost Levels
Level memorisation and warp routing are half the battle
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.