Thanks Noel! Heh, waaaay back in the day... the original costumes for the FFD cast were primarily based on their FF4:TAY sprites. This was before I joined the development team and before William and I decided to just go all in and get custom sprites done as well. This is why so many of the playable characters have undergone multiple drafts. It's been a big pain doing constant revisions, but I'm glad I finally have full creative control over the original character designs.
I went with the SOLDIER outfit simply because it matched Cid's original battler (take a look and you'll see the resemblance). Eventually, it just stuck. I think it actually suits him pretty well.