The practical consequence here is that this fight gets decided in the back half, and that's Benn's half. If Garcia's output drops around 30% after round four, then every round from five on is Benn walking him down while Garcia looks for one counter. That's not a coin flip, that's a trend.
And your efficiency argument is clever but it's circular. You're assuming the early finish to prove the early finish. Arena HVAC load doesn't decide fights, and if Garcia doesn't land that left hook clean in the first four rounds, the efficiency story evaporates and you're left with a fading fighter against a guy who never stops.
Benn's pressure is systematic, not reckless. Body, head, body, keep the guard dropping. You can't counter what you can't time, and tired fighters don't time anything.
So yeah, fast hands are real. But real fights get ugly after round six, and that's where Benn lives.