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 · Competitive PvP
A hip-hop themed brawler where customized fighters batter each other through New York clubs.

Execution · Practiced Mastery
The sequel adding Horde mode to the campaign-plus-versus cover shooter formula.
Def Jam: Fight for NY leans Execution (Competitive PvP); Gears of War 2 leans Execution (Practiced Mastery).
Gears of War 2 leans a little harder on execution, though the gap is small.
Def Jam: Fight for NY
Combo timing, grapple inputs, environment slams demand solid hands.
Gears of War 2
Gnasher battles and movement tech set the ceiling
Def Jam: Fight for NY leans a little harder on reads, though the gap is small.
Def Jam: Fight for NY
Versus humans, baiting grabs and counters matters; AI is mappable.
Gears of War 2
Human opponents in versus drive prediction play
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Def Jam: Fight for NY
Minor stage and AI behaviour randomness.
Gears of War 2
Horde spawns add mild randomness
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Def Jam: Fight for NY
Fighting-style blends, move purchases, venue weapons reward system knowledge.
Gears of War 2
Power-weapon timing and positioning are solvable
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.