Well, I think I got rid of the black screen by deleting "steam_api64.dll" in the FFXIV\boot folder. The game was able to load and quit this time after without getting stuck in a black screen. At first I was renaming the SteamClient64.dll from my Steam folder, which worked just as well but would get downloaded again whenever Steam restarts.

I am unsure on what steam_api64.dll does but it was causing me problems so I'll probably have to delete it every time it gets downloaded, hoping it doesn't cause any problems.

Only time will tell if this truly was the problem.