Regarding the Pictish Warrior, I can't help but feel people are overriding common sense based on possibly dodgy information.
While it's true that in the picture, iron working hasn't been researched yet, it' also quite probable that the picture was made in some sort of worldbuilder, and the devs can spawn anything they like for the purposes of demonstration. Given that the Celts are shown to have a green colour scheme in the Machine Gun picture, yet the Pictish warriors here are blue, it's quite possible the Picitsh Warrior in that picture doesn't belong to the Celts at all, but the picture is entirely staged.
I simply think that it doesn't make sense for the Pictish Warrior not to replace the Swordsman, not simply because it is quite clearly carrying a sword and shield, but because it has the same stats (unless they're changing the stats, of course). What is the point of making a Spearman or Pikeman replacement that acts like an ironless Swordsman? Not only does it make the bonus vs mounted units nonsensical, it makes building regular swords utterly useless.
If they wanted to give the Celts a sword that didn't need iron (which I would be baffled as to why they would anyway), they could just go the Mohawk route and make it a unique Swordsman that simply doesn't need iron.