You can always switch between FFXIV and WoW, noone is forcing you to play one of them specific, hell a lot of Blizzard staff have admitted that they play FFXIV and they show it on their Twitters aswell, and the lead developer of FFXIV (Yoshida) visited Blizzard a lot of times and they gave him some miniatures and other stuff
Both games are very successful and they marked themselves in history no matter what happens, completely deleting your WoW or Battle.net account is never a good idea (you will regret it hard later) and its extremely hard to do it in the first place if not impossible, you have to find other ways to reduce your addiction.