The mob spawns and whatnot, their synching of your client and world server is all done on a Data Center level server, meaning everyone on your data center used the same one as you. The servers function in multiple entwined layers, each serving different functions, if this has only been occuring recently, like since the NADC upgrade its highly likely the cause. The invisible char and mount model/texture is very much a congestion issue, the visuals of your character are saved on a separate database, that is connected by the data center server that synch information from your client to your world server and to all other sever based game aspects. Our clients hold limited information in MMORPG's, what we generate ourselves is the terrain, UI, sounds, and the base cut-scenes (everything except our and others character visual data)

Sound queues for activated skills and abilities as well as their animations come yo our clients externally, its why when there is a server side 'hiccup' as it were we tend to experience that fast forward effect. The world map specifically has a modified world map version now, when clicking on a quest for a location the new map will show, which is very generic, but has connecting lines to each zone change but also shows just the erythrocyte. The response lag you have is very much classified as 'server lag', as the synching from your client input to the game server is lagging.stressing.

If you want to do some tests... I see you have Win8, I applaud you for not going to 10, im a 7 user myself, My system is a bit better than yours, AMD FX8350 4.0ghz (close to 4 ears old too but higher end), 16gm RAM, GTX 1070 FTW2, several WD- Black 1TB (no raid) -- I mention this because I have experienced similar issue and run the game on max with 60-120 FPS during play on my 1080p 23" LCD monitor. More specifically to the testing, Open the Run command likely found in your start menu, open it and in the text imput line type: resmon.exe

Then click 'Ok'

--Once running, on the Overview tab check the box on the CPU section that has the game application, ffxiv.exe for the dx9 32-bit client or ffxiv_dx11 the 64-bit client.
--Once that is done, select the Network tab and you will see two instances of the game application listed, if you are at char select or start screen there will be only one, once you log in you will see two.
--They should be similar in number on the latency column, go ahead and drag shrink the other columns, they are insignificant.
--During play take note of the numbers, the moment you begin to experience these issue take a look, one of the latency values should be much higher than the other.

** I personally have two monitor to work with, if you only have a single display for this test, run the game in windowed mode and shrink it just enough to see the values, walk around use anthers, don't need to do any combat as running in windowed may be difficult.

If you feel up to doing this you can post back your highs and lows and shat happens when you experience these slow downs, I predict one will spike over the other.