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 · Pure Optimization
A tower defense testing optimal tower combinations against scripted waves.

Optimization · Pure Optimization
The genre-defining cartoon tower defense with crunchy upgrades and fixed waves begging for perfect solutions.
Element TD 2 leans Optimization (Pure Optimization); Kingdom Rush 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.
Element TD 2
Light micro on tower placement timing, minimal twitch
Kingdom Rush
Light micro of hero and rally points
Element TD 2 leans a little harder on reads, though the gap is small.
Element TD 2
Scripted enemy waves, no adaptive opponent
Kingdom Rush
Wave compositions are fixed and previewable
Element TD 2 leans a little harder on variance, though the gap is small.
Element TD 2
Wave composition known, little hidden information
Kingdom Rush
Almost fully deterministic waves
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Element TD 2
Optimal tower combos and placement IS the game
Kingdom Rush
Tower placement and upgrade routes 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.