Define terms first: "wins" means whose hand gets raised under boxing rules. That framework settles this, because the practical consequence of picking Benn is that you're betting on a shorter, shorter-armed pressure fighter closing distance on a longer, faster, harder-hitting counterpuncher. That's the hardest job in the sport.
Garcia's reach and hand speed mean Benn eats shots on the way in. Benn's durability is the real issue. He's been visibly hurt and dropped by opponents who don't punch like Garcia does.
Yes, Benn's path is real: relentless inside work and body shots over twelve rounds. I'll grant that. But Garcia's check hook and straight right land first, and length plus speed plus power usually beats pressure when the pressure fighter can't absorb the shot. So Garcia wins.