I did some more experimenting, no need to rename/remove steamclient64.dll in the Steam Folder.
Instead, I renamedinsideCode:steam_api64.dll
toCode:<Steam Folder>\steamapps\common\FINAL FANTASY XIV Online\boot
That seems to consistently work for me, and it persists through Steam restarting. I'm assuming it will work until FFXIV pushes an update for that file. Again, not sure what the consequences are, but it allows me to play the game without quitting Steam.Code:steam_api64-bak.dll