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 · Competitive PvP
Vietnam-era large-scale multiplayer shooter mixing infantry firefights with helicopters and jungle ambushes.

Execution · Pure Mechanics
Fast arena-style shooter mixing a scripted Strogg campaign with twitch multiplayer.
Battlefield Vietnam leans Execution (Competitive PvP); Quake 4 leans Execution (Pure Mechanics).
Quake 4 leans a little harder on execution, though the gap is small.
Battlefield Vietnam
Gunplay, vehicle handling, and helicopter piloting
Quake 4
Aimbot plus strafe-jump inputs dominate both campaign and multiplayer
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Battlefield Vietnam
Human squads flank and contest objectives unpredictably
Quake 4
Multiplayer duels reward predicting human positioning and timing
Battlefield Vietnam leans a little harder on variance, though the gap is small.
Battlefield Vietnam
Spawn waves and vehicle availability shuffle fights
Quake 4
Spawn and item timing add mild uncertainty
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Battlefield Vietnam
Map control, loadouts, and ticket-bleed knowledge
Quake 4
Item control routes and weapon picks are learnable
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.