I think you will find most people are kind of relaxed about the WYSIWYG rules, if your guys look Roman then they will do. I've seen hopolite pretending to be pikemen and worse.
Romans carrying Swords will certainly be fine. Its probably more accurate anyway.
"Religious wars are basically people killing each other over who has the better imaginary friend" -Napoleon Bonaparte
In my area we are not WYSIWYG. In your example Pila would be assumed - we explain as we set up what is being fielded. Same for spear armed cavalry that get a Javelin upgrade - we don't insist on figures modelling both - just state when placing the unit.
The only one I myself like to properly model is shields - that has the biggest visual difference in my view.