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
A pioneer of action-MMORPG combat where skill-shot execution and precise dodges are the primary test.

Execution · Practiced Mastery
Co-op-focused action sequel hurling Titus against Tyranid swarms with parry-heavy melee combat.
TERA leans Execution (Practiced Mastery); Warhammer 40,000: Space Marine 2 leans Execution (Practiced Mastery).
TERA leans a little harder on execution, though the gap is small.
TERA
Action combat with skill shots and iframe dodges is the core axis
Warhammer 40,000: Space Marine 2
Parry, dodge and gun-strike timing against swarms
TERA leans a little harder on reads, though the gap is small.
TERA
Battlegrounds and large-scale PvP add a real but secondary reads layer
Warhammer 40,000: Space Marine 2
PvP Eternal War adds some human prediction
TERA leans a little harder on variance, though the gap is small.
TERA
Gear enchanting RNG creates frustrating hidden-information variance
Warhammer 40,000: Space Marine 2
Tyranid swarm spawns vary run to run
TERA leans a little harder on optimization, though the gap is small.
TERA
Class rotations and gear progression paths are extensively community-solved
Warhammer 40,000: Space Marine 2
Class builds and perk loadouts reward planning
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.