I feel like one of the most undisputed downsides of any private server vs retail is the server staff also playing on the same server. Favoritism, biases, friend group advantages when it comes to content, all the way to selling gil to players to name a few. All of this is enough to deter myself and many others.
I actually love the fact that a GM on Wings gave himself a billion gil and then sold it to players. I dunno if its illegal in real world terms but in game terms, i find it hilariously genius.