Less air flow is less air to compress in the first place.
Easier to make power through large amounts inefficient fuel and air than highly efficient but very little fuel and air, the efficiency range for our type of engines aren't that huge. 1.4-1.67 lbs-ft per cid is an efficiency most of us won't see that's 445-530 lbs-ft for a 318, no one here would say 318 is the engine you need if looking to make 500 lbs-ft they build an inefficient 408 (1.23 lbs-ft per cid) instead :)
