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.

Execution · Competitive PvP
A tactical shooter where precise gunplay against human opposition is the deciding skill.

Execution · Pure Mechanics
Tests twitch aim and physics-prop improvisation against human opponents.
Counter-Strike: Condition Zero leans Execution (Competitive PvP); Half-Life 2: Deathmatch leans Execution (Pure Mechanics).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Counter-Strike: Condition Zero
aim and spray control decide duels
Half-Life 2: Deathmatch
Aim, movement and gravity-gun catches decide every duel
Counter-Strike: Condition Zero leans a little harder on reads, though the gap is small.
Counter-Strike: Condition Zero
predicting human opponent positioning
Half-Life 2: Deathmatch
Predicting human spawns, dodges and prop throws matters constantly
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Counter-Strike: Condition Zero
buy-round economy and drops vary slightly
Half-Life 2: Deathmatch
Physics props add minor situational chaos
Counter-Strike: Condition Zero leans a little harder on optimization, though the gap is small.
Counter-Strike: Condition Zero
economy management and utility usage solvable
Half-Life 2: Deathmatch
Weapon spawns and map control are learnable layers
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.