Aesthetics isn't something you can make an exact quantification of. It's all a matter of artistic sensibility and cultural focus. The only way to evaluate it is to ask many people how much they feel touched by a certain piece of art or, in this case, by the game's environments and overall design. Evidently, many FFXIV users are criticizing exactly the world's environments and their design, meaning the game has poor aesthetics. There's really not much that can be added. A few good looking armor sets and items won't affect the game's aesthetics, like adding two pretty flowers to a boring green field won't make a painting interesting. It's a much more general matter and i can't see a clear way to solve it.