Just a few words about Phalanx and Syntagma formations from what I experienced in Sybillae Vox. Remember my mod is way slower and have a bigger focus on unit positionning.
The Phalanx is not deep, usually 2 to 4 lines in the games I played. Considering the spear range, the first two lines are fighting, the deeper lines are there for formation durability (it could add a push bonus like an attack bonus for the first line anyway). So disrupting a spear line can be rather quick by making a hole in the middle.
The Syntagma is deep, 4x4 for the minimum requirement (that I made). The pike is way longer so almost everybody is fighting, at least the 3 front line. Put a Syntagma in an open door and none shall pass for example. This is especially true against swordmen who have even shorter range (not in the vanilla game), they just get impaled before getting in range. Individually pikemen are almost useless but get a strong bonus when in Syntagma (or lesser in a line/phalanx).