I think an improvement to the system would be to rename retainers without using a fantasia. I have 8, and if I want to rename them all, I have to strip all of them of their gear, try and manage a completely full inventory to know who wore what, and click through character creator just to fix a typo or give them a new name.

I think name changes could work like Chocobo where they just need to not be in action to do so. So not on a venture. For people that only have 1 or 2 retainers, the process may be much easier, but it is still a process.