FFXIV is the most casual friendly sub MMO out there for the most part. Albeit, with the DC travel that might change a bit due to Aether and other savage raider servers sort of setting the tone now. Generally, the problem areas FFXIV has are sort of the same as with other MMOs. Extremely strict content that requires a lot of precision to complete generally is bad for long form experiences because of building frustration: Either someone gets frustrated by lack of progress in PF, or in statics the habits and social quirks jade on people as they grind out fights and people shuffle between different statics. And then most other types of content at end game end up to be grinds that never end or take forever.

I'd say the community of FFXIV generally starts having social health issues after the first year of an expansion and generally from those who have been through one too many grinds.