You ought to clarify what you mean by "inefficient".

Do you mean less capable of turning a pound of fuel into an hour of horsepower,
or do you mean less capable of making of making high horsepower at high rpm?

The 360 has relatively large main bearings,
which may be good for low rpm heavy torque towing duties.

This beefed up lower end also makes it about 57 lbs heavier than a 318,
but race shops like Petty Enterprises found plenty of places on the stock block to machine away unnecessary and non-load bearing weight.

Nearly all the American V8 manufacturers found that Honda's redesign of main bearing were both smaller, less friction and capable of higher rpm.

The internally balanced 318 has one of the highest rod/stroke ratios which has inherent low friction advantages,
and can allow slightly higher dynamic compression rations. The 360 is only slightly less.

For high rpm horsepower production,
cylinder head breathing mostly dominates,
and valve size (and number) in turn is very important.

Canted and opposed (Hemi) valve arrangements
allow larger diameter valves
and straighter runners
than side by side valve Wedge designs
in cylinders of the same diameter,
so a 5.7 Hemi has a high rpm breathing advantage
over a Magnum 5.9 Wedge.

When comparing pickup truck duty
Magnum 5.2 to Magnum 5.9
the dominant thing is the beer barrel intake manifold,
which was designed for the 5.2
and when this 15.5 runner length intake manifold is bolted unmodified on a 5.9
brings peak torque and horsepower in at lower rpms.

Drag racers consider this as choking off performance above 4000 rpm.

For working pickup truck use
available low rpm torque is a good thing.

If you want to fault a particular feature of both 5.2 and 5.9 V8s,
one very questionable area is:
why are the
Quench clearances of piston to head
so much larger than 0.026 inches,
(0.047 plus 0.055)
and why are the factory dynamic compression ratios so relatively low?

The probable answer is that
cylinder to cylinder quality control at the factory
was so variable
that a large average Quench clearance was necessary
to keep "statistical outlier"
tight cylinder piston fits
from hitting the cylinder head
and generating a costly to Chrysler warranty claim.