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
Pure aim and movement skill tested against adaptive human opponents competing for spawn-cycle dominance.

Execution · Competitive PvP
A boxing game testing punch timing and reading opponent openings.
Quake III Arena leans Execution (Pure Mechanics); Real Boxing leans Execution (Competitive PvP).
Quake III Arena leans a little harder on execution, though the gap is small.
Quake III Arena
Rail and rocket aim at speed is the entire game
Real Boxing
Timing punches, blocks and dodges is the core
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Quake III Arena
Human opponents adapt their routes and timings in direct response
Real Boxing
Reading opponent feints matters in multiplayer
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Quake III Arena
Spawn locations have mild randomness but are quickly mapped
Real Boxing
Little randomness in outcomes
Quake III Arena leans a little harder on optimization, though the gap is small.
Quake III Arena
Armor and weapon timing routes are learnable and highly leveraged
Real Boxing
Stat training and stamina management add depth
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.