Bret Devereaux

Oh, substantial disagreement there. Mao has this right: the weaker party needs to trade space for time and attrition. Prohibitive defenses are the luxury of a side that enjoys substantial overmatch.

Conventional warfare is very different from guerilla warfare, though. In particular, attrition is a percentile game. If you have insufficient firepower up front, then they are biting off much larger portions of your forces than you are attriting theirs.

The biggest factor here in modern warfare is that only a small percent of an attacking force can be brought to bear as long as the front holds. A BEF division on the Somme only has 16 platoons in the actual firing line and this can be matched by a regiment.

This may not be the case anymore! Azerbaijan/Armenia war made heavy use of drone-spotted artillery (also suited rough terrain). Indirect, drone-spotted artillery could make the self-propelled howitzer the fundamental unit of war in the 2020s

Indirect fires are already the fundamental unit of war (since '15), issue is that infantry still has to be flushed out of cover in order for the artillery to kill it. The French dropped tactical nukes worth of explosive per division at La Malmaison and still had hard fighting.

True, but the balance swung quite a bit between fires and maneuver, which was arguably the dominant element of WW2 in most theaters

Yes and no. WWII was still, IMO, a fires war. Unit collapse only ensued after a frontline had been decisively broken, and that was mostly a fires and positional fighting situation. The Eastern Front was very much a trench war, for example.

Fires are certainly a big part, but strategic encirclements like Dunkirk in 40, Barbarossa cauldrons in 41, or the Stalingrad encirclement in 42/43 seem very maneuver-oriented. German maneuver warfare and Soviet deep battle also matter, Western doctrine seems more fires-focused.