Bret Devereaux

Whereas I am quite confident that by the 160s BC, mail was the majority armor-type of the Roman heavy infantry.

What was the harder formation to emulate? The Roman cohort structure of heavy javelin/big shield/stabby stab - or - sarissa phalanx?

I'm with @DrMichaelJTayl1 - it's the legion. The necessary equipment is more expensive and you have to train and prepare for a greater degree of local decision making Sure a file-leader leads his file, but how many units in a phalanx you have individually maneuvering?

Alexander's pezhetairoi had 6 taxeis which might maneuver independently, plus the hypaspists. But assuming we buy the standard cascade attack of the legion (and I think we should), every maniple of a legion can maneuver separately.

So you have that triplex acies w/ potentially thirty separately maneuvering blocks of men per legion, doing substantially more complex maneuvers than the sarissa-phalanx was typically capable of. The number of guys you need who can 'drive' a unit around the field is much higher.

But are those individual pieces doing that much? Attack. Withdraw. Fall back. Each officer is not maneuvering based on the entirety of the battle, but rather their immediate circumstances. Each syntagma probably weighed similar concerns.

I mean, both Cynoscephalae and Pydna are fatal to this argument though - in both cases, the Romans are effectively able to maneuver maniples independently and win as a result, and the Antigonids can't, and lose.

You might argue that the Antigonids just suck, but its the explicit testimony of Polybius - hardly a friend to the Antigonids - that they had the best man-for-man quality phalanx around. Which seems supported by how far above their weight they punch vs. Seleucids and Lagids.