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

Execution · Practiced Mastery
Aim and spawn memorisation through a fully scripted cinematic campaign.

Execution · Pure Mechanics
Wrestling motion-control aim and swordplay through fixed scripted shootouts.
Call of Duty: Modern Warfare 2 Campaign Remastered leans Execution (Practiced Mastery); Red Steel leans Execution (Pure Mechanics).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Call of Duty: Modern Warfare 2 Campaign Remastered
Aim and reaction carry every scripted firefight
Red Steel
Wiimote aiming and sword swings are the whole physical test
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Call of Duty: Modern Warfare 2 Campaign Remastered
Enemies spawn and behave on fixed scripts
Red Steel
Enemies are scripted spawns, never adaptive
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Call of Duty: Modern Warfare 2 Campaign Remastered
Set-piece campaign with almost nothing random
Red Steel
Encounters are fixed once seen
Call of Duty: Modern Warfare 2 Campaign Remastered leans a little harder on optimization, though the gap is small.
Call of Duty: Modern Warfare 2 Campaign Remastered
Learning spawns and cover lines trivialises veteran difficulty
Red Steel
Light level memorisation and weapon choices
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.