Colorful gets it. PCs allow you downgrade the visual settings very easily, many games come with both HD graphics & standard. FFXIV is theoretically anything but taxing graphically, *however* the engine & way it is implemented means that it taxes hardware it shouldn't. I was going to give a car analogy but realised that most Americans don't drive manuals.

Right now the game has graphics proven to have been directly imported from previous PS3 FF games. Importing is usually far less optimised than building a model from scratch for a new system. Ironically, better quality tends to use less resources! Just look at Windows 10, it runs on PCs far less powerful than 8.0 required, heck, it even runs on phones that could barely load 8.1 (which had to be significantly cut down to run at all).

TLDR: A graphics update, done properly, will probably run better on your low to mid tier hardware than the current low quality does as it will be more optimised.