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

Optimization · Pure Optimization
A deep tower defense about popping waves of balloons with monkey towers.

Optimization · Pure Optimization
A physics puzzle of engineering Rube Goldberg contraptions to solve fixed goals.
Bloons TD 6 leans Optimization (Pure Optimization); The Incredible Machine 3 leans Optimization (Pure Optimization).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Bloons TD 6
Placement clicks only; no dexterity ceiling
The Incredible Machine 3
Placing parts is untimed, no dexterity needed
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Bloons TD 6
Bloon waves are fixed and known
The Incredible Machine 3
Solo puzzle, nothing to predict
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Bloons TD 6
Wave order is deterministic; tiny targeting randomness
The Incredible Machine 3
Physics is deterministic, no randomness
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Bloons TD 6
Tower placement, upgrades, and economy are near-solvable
The Incredible Machine 3
Engineering a working contraption from parts IS the 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.