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

Optimization · Practiced Mastery
Active dodge-heavy combat with a deep build system, tested against both scripted content and human opponents.

Optimization · Practiced Mastery
Planning a raid in advance, then executing it where one mistake kills.
Guild Wars 2 leans Optimization (Practiced Mastery); Tom Clancy's Rainbow Six 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.
Guild Wars 2
Dodge timing and active combat define moment-to-moment play
Tom Clancy's Rainbow Six
One bullet kills, so entries demand clean aim
Guild Wars 2 leans a little harder on reads, though the gap is small.
Guild Wars 2
WvW and structured PvP feature real adaptive opponents
Tom Clancy's Rainbow Six
Multiplayer raids add human counterplay
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Guild Wars 2
Loot RNG is present but secondary to skill expression
Tom Clancy's Rainbow Six
Terrorist placements are unknown until doors open
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Guild Wars 2
Build crafting and rotation theory-crafting reward deep analysis
Tom Clancy's Rainbow Six
The pre-mission planning phase is the real game
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.