head to head
Neither is simply harder - they are hard in different places. Kerbal Space Program demands more execution; Rome: Total War demands more reads.

Optimization · Pure Optimization
Rocket engineering sandbox about orbital mechanics.

Optimization · Pure Optimization
A landmark strategy game combining a turn-based campaign for control of Rome with massive real-time battles.
Kerbal Space Program leans Optimization (Pure Optimization); Rome: Total War leans Optimization (Pure Optimization).
Kerbal Space Program leans clearly harder on execution.
Kerbal Space Program
Manual piloting, docking precision
Rome: Total War
Real-time battle micro rewards quick unit handling
Rome: Total War leans clearly harder on reads.
Kerbal Space Program
No adaptive opponents
Rome: Total War
Optional multiplayer battles; campaign AI is mappable
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Kerbal Space Program
Light reentry and physics variance
Rome: Total War
Diplomacy and AI moves add modest fog
Kerbal Space Program leans clearly harder on optimization.
Kerbal Space Program
Rocket design, delta-v budget, mission planning
Rome: Total War
Campaign economy, recruitment, and battle tactics 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.