This is a major issue, I have done this FATE many of times and it can be a pain to see the main dragon. If your in a group you can just help with the small adds by staying in the back and get full credit, but that is not what you want to do.

I normally see just Chocobo companions and SCH/SMN pets fighting the boss if I go near it, and risk a death since I have no idea where the boss is facing and also do not see his AoE because hes not visible or targetable by me.

The priority for loading in is off for sure, and it should be fixed in time, hopefully sooner than later.