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
The sequel adding Horde mode to the campaign-plus-versus cover shooter formula.

Execution · Practiced Mastery
Browser tank duels mixing aim, human positioning reads, and upgrade grind.
Gears of War 2 leans Execution (Practiced Mastery); Tanki Online leans Execution (Practiced Mastery).
Gears of War 2 leans a little harder on execution, though the gap is small.
Gears of War 2
Gnasher battles and movement tech set the ceiling
Tanki Online
Aiming turrets and dodging shells decides duels
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Gears of War 2
Human opponents in versus drive prediction play
Tanki Online
Human tankers feint around corners and flag routes
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Gears of War 2
Horde spawns add mild randomness
Tanki Online
Spawns and drops add light battlefield noise
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Gears of War 2
Power-weapon timing and positioning are solvable
Tanki Online
Equipment upgrades and loadout economy gate the grind
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.