Its quite simple, he is talking about loading lag, which is the long times it takes to load things like initialy starting the game and character models, which are stored on the client's PC, when the game starts it has to load the huge zones from the HDD, and even the character models it just gets the information for the PC to build the models for example if there is a hyur midlander male with face 2, large body size, a scar on the left eye, brown hair 1 etc etc, this is what the client recives from the server, then the client builds all character models onscreen using that information.
Because of this loading from even a 7200RPM HDD takes time because of the physical limitations of a HDD which when the cost of SSDs come down HDD will be obsolete, yes the client could do with optimising which I will not deny, but loading lag is either HDD read speed, CPU clock speed because or graphics card rendering speed.
Most of what you mentioned are networking problems, but if you look at the network indicator ingame, you will notice not much bandwidth is used by the game, take a character model that usually only takes about 5Mb to download because its the client that draws them.
Btw, if a HDD is almost full the loading lag isnt affected that much, the main problem there could be from a full HDD is fragmented data, because the CPU knows where information related to programs should be even with a full HDD, the CPU knows where all FFXIV data should be when you open the patcher, because the programs are connected.
You are just somone that thinks they know everything, people have taken my advice on a SSD before now and have seen large loading lag reductions, believe me when I have the money I will be getting a SSD when I have the money, even if it is just a small one to put windows and FFXIV on, which is all you need.
My profession makes me need to know how to diagnose problems based on little information, and because the op posted about loading lag, and said they have a decent PC, it is the most logical fix to invest in a SSD because the game has to load so much information from the HDD on the fly, if the op has a SSD I would then suggest a CPU upgrade because of the need for multitasking to play this game.
Also here you mention 6GB as a good amount of RAM which is true but unless you run graphics design software of virtual machines, or other RAM intensive software you dont need it, RAM only slows a system down if you are topping it out by running multiple programs at once for example I have 8GB of RAM in the laptop I play FFXIV on when the system is running just firefox skype and background programs I am using 1.62GB of it therefore I will not notice a slowdown just running FFXIV on top of those, however with 2GB of RAM I would notice a slowdown because the system would be page filing so my system does not crash.
The only way I top out my RAM is when I am running 5-6 virtual machines which I do.
If you want to see the problem page filing has, top out your RAM, and you will notice the symptoms of topped out RAM, 3GB+ RAM you will not notice a slowdown, and it will definatly not increase loading times, and if you have any less than 3GB RAM you should really upgrade.