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 · Practiced Mastery
A cover-shooter Rainbow Six blending tactical room-clearing with solid gunplay.

Execution · Practiced Mastery
Artillery aim under wind combined with fort economy planning against human opponents.
Tom Clancy's Rainbow Six: Vegas 2 leans Execution (Practiced Mastery); Worms Forts: Under Siege leans Execution (Practiced Mastery).
Tom Clancy's Rainbow Six: Vegas 2 leans a little harder on execution, though the gap is small.
Tom Clancy's Rainbow Six: Vegas 2
Cover-based gunfights still punish poor aim
Worms Forts: Under Siege
Manual trajectory aiming under wind decides each shot
Worms Forts: Under Siege leans a little harder on reads, though the gap is small.
Tom Clancy's Rainbow Six: Vegas 2
Multiplayer brings some human adaptation; AI is scripted
Worms Forts: Under Siege
Human opponents to outguess on building and target priorities
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: Vegas 2
Enemy placements partially unknown per encounter
Worms Forts: Under Siege
Wind, crates and terrain damage randomize turns
Tom Clancy's Rainbow Six: Vegas 2 leans a little harder on optimization, though the gap is small.
Tom Clancy's Rainbow Six: Vegas 2
Room-clearing order and squad commands are solvable tactics
Worms Forts: Under Siege
Fort placement and weapon-tech economy reward planning
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.