The Primary Weapon, Spear or Sword?

[Caballo]

I think the key evidence for the spear being pre-eminent in the later period is in the missoria, showing spears, but very few swords being worn.
For example




Not a sword or a scabbard or chape end to be seen worn by the simple pedes, though worn by the Emperor or displayed in front of the troops (in the Valentinian example).

Clearly swords were still around, but I suggest that economics made them rarer. Also IIRC, and based on the Miks book, many more swords appear to have survived from earlier periods (though I accept that this is a dodgier piece of evidence).

Cheers

caballo