It seem to me that gear usually drop for class that perform best in group. Not sure what happen if there are multiple players of same class, maybe it is random number for need but maybe based on damage dealt etc.
Basically if you do your job good your chances are better to get the gear you need.
So my evil advice would be to get good (or better) at what you do. I know I still find new ways how to perform better on my jobs even 6 months after I started to play ff xiv and I couldn't get gear drops by using just 1 combo as lancer for example.