head to head
Neither is harder. They score identically on all four axes, so the difference between them is in kind, not degree.

Optimization · Practiced Mastery
Planning a raid in advance, then executing it where one mistake kills.

Optimization · Practiced Mastery
A tower-defense hybrid testing turret placement, economy and hands-on aiming.
Tom Clancy's Rainbow Six leans Optimization (Practiced Mastery); Toy Soldiers: War Chest leans Optimization (Practiced Mastery).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Tom Clancy's Rainbow Six
One bullet kills, so entries demand clean aim
Toy Soldiers: War Chest
Manning turrets adds aim and reaction demands
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Tom Clancy's Rainbow Six
Multiplayer raids add human counterplay
Toy Soldiers: War Chest
Enemy waves scripted; multiplayer adds some prediction
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Tom Clancy's Rainbow Six
Terrorist placements are unknown until doors open
Toy Soldiers: War Chest
Wave variety and unit outcomes add modest randomness
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Tom Clancy's Rainbow Six
The pre-mission planning phase is the real game
Toy Soldiers: War Chest
Turret placement, upgrades and economy drive defense
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.