The real problem with the "look" of the gear is the time period they set the clothing in. They've chosen a more medieval time period (like the real world medieval, not medieval fantasy as in the genre). If you've looked into this time period most of everything worn was either draped loosely (ie: cowls and turbans, one piece of fabric clothings) or consisted of dull chain or plate metal (ie: chain mail and plate mail with very little design or "flair").

While on the other hand:

Final Fantasy XI, uses more of a renaissance time period where the clothing was more intricate and more fabrics used patterns, also chain/plate mails had etching and intricate designs on them. In turn we can see in XI's gear more designs on the actual articles of clothing. With this they were able to create more visually appealing pieces of armor/clothes.

What I hope happens to XIV:

Personally I hope they run from their initial concept of "Medieval attire" and develop a new armor/clothing concept so we can have more visually appealing stuff to equip, now I know you say its just a guideline and yes I would have to agree there are some armor that is not truly "medieval" but the lack of color and design (not texture) on the armor still keeps it in that time period.

As a graduate student who has designed clothing articles for both said time periods, I hope this sheds some light on the lack of good looking armor.

PS: Its quite possible for them to get a new concept design for when an expansion rolls around (after all they did it in FFXI)