I suspect there has been, since ancient times, two "classes" of soldiers: the 'warriors' (and the 'gentlemen warriors' who led them into close combat) and the "professionals." I'm sure that every Roman centurion knew, roughly, how deep and wide each layer of a road had to be, but the big roads and the aqueducts were built by trained engineers and the Romans also had specialist to operate the catapults and so on. The gunpowder age added to the "professionals" status; some Scots lords, for example, had more artillery in their private arsenals than King Henry VIII had in his entire army. Gunners, sappers and miners and other specialists were the core of the "standing army" while the bands of warriors - led by gentlemen - were called up as needed.
Many of my gunner friends who were FOOs in a combat team do not believe they played "second fiddle" to the infantry or armoured corps soldiers who marched (or rode) beside them. Ditto the sappers who want ahead to clear obstacles so that the infantry and armoured soldiers could follow.
