Biggest turnoff for the newcomers that I have met are:

1. Boring gameplay, for most of the classes untill you become level 30, you only use 2-3 skills max. WHM was my first class to reach level 30 and doing Stone and Aero was very boring. It does not help that ARR mobs were very easy to kill and do not do alot of damage (they fixed it for HW content though)

2. Story takes its time to develop and there are alot of fetch quests. Minfilia gives you an Eorzea's version of mobile phone and she never uses it to receive your mission report.

3. The rush crowd. One of the things that I dislike when doing a dungeon as a Mentor with another max level player and 2 newcomers is seeing that max level player push around the newcomers, so he/she can finish the dungeon run fast. Newcomers learn nothing, they do not get to enjoy the content and often they get bullied for being new to the content. When it comes to toxic community, FFXIV is a better community then World of Warcraft and League of Legends, but if you look at what happens both ingame and on the forum, you see a rise of toxic behavior.