Sadly yes. The only one "special formation" per units, it is even called special ability in R:TW as in any RTS, where units just have such things for gameplay reasons, not to simulate their historic capabilities.

I only gave the polybian Triarii the schiltrom formation in my personal version. For me it seems to be more usefull if the Hastati and Principes are routed/had to retreat and I like to have all tactical possibilities of their historic counterparts somewhere in my armies.