head to head
Neither is simply harder - they are hard in different places. Fallout: New Vegas demands more execution; The Battle for Wesnoth demands more variance.

Optimization · Pure Optimization
A faction-driven RPG-shooter where build and route planning shape every ending.

Optimization · Pure Optimization
An open-source hex strategy game famous for its luck-laced combat rolls.
Fallout: New Vegas leans Optimization (Pure Optimization); The Battle for Wesnoth leans Optimization (Pure Optimization).
Fallout: New Vegas leans clearly harder on execution.
Fallout: New Vegas
Shooter inputs with VATS assist
The Battle for Wesnoth
Turn-based hex moves, no dexterity.
The Battle for Wesnoth leans clearly harder on reads.
Fallout: New Vegas
Scripted factions and enemies
The Battle for Wesnoth
Multiplayer opponents adapt; campaigns scripted.
The Battle for Wesnoth leans clearly harder on variance.
Fallout: New Vegas
Some loot and crit RNG
The Battle for Wesnoth
To-hit rolls swing battles constantly.
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Fallout: New Vegas
Faction routing, perks, builds heavily rewarded
The Battle for Wesnoth
Unit matchups, terrain, and economy 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.