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

Execution · Practiced Mastery
The console FPS landmark that introduced Master Chief and the ring world.

Execution · Practiced Mastery
A cover-shooter Rainbow Six blending tactical room-clearing with solid gunplay.
Halo: Combat Evolved leans Execution (Practiced Mastery); Tom Clancy's Rainbow Six: Vegas 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.
Halo: Combat Evolved
Aim, grenade timing, and vehicle control
Tom Clancy's Rainbow Six: Vegas 2
Cover-based gunfights still punish poor aim
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Halo: Combat Evolved
Multiplayer duels reward reading humans
Tom Clancy's Rainbow Six: Vegas 2
Multiplayer brings some human adaptation; AI is scripted
Tom Clancy's Rainbow Six: Vegas 2 leans a little harder on variance, though the gap is small.
Halo: Combat Evolved
Covenant AI varies tactics slightly
Tom Clancy's Rainbow Six: Vegas 2
Enemy placements partially unknown per encounter
Tom Clancy's Rainbow Six: Vegas 2 leans a little harder on optimization, though the gap is small.
Halo: Combat Evolved
Weapon sandbox knowledge and encounter routing
Tom Clancy's Rainbow Six: Vegas 2
Room-clearing order and squad commands are solvable tactics
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.