As a player, the only time I have a problem with app rejections is when they feel just arbitrary, rather than actually serving a purpose.
More than one MU I've been on has had a lot of 'unstated rules' about their applications that end up being endlessly frustrating. Stuff like, 'Hey, you compared your character's attributes to existing characters in the fiction that are literally used as attribute benchmarks IN THE FICTION, we don't allow that. And no, we didn't tell you that ahead of time. Rewrite everything.'
Or 'Um, I personally don't like character type X and think it's overdone. No, it's not on the banned or restricted list, I just feel like I need to make a stand on YOUR app, as opposed to anybody else's. And no we don't need to update the banned or restricted policies, I'm just talking to you.'
Or 'Your character is a little too political.' With 'political' being a euphemism for 'character type based on a group that makes me uncomfortable in real life'. In a modern game. (Note, I'm not talking about making a Nazi character here, just somebody who was a mutant rights activist, on a game about Marvel mutants.)
When the rejection makes sense and doesn't feel arbitrary, I'm fine with it. But with no offense intended to staffers out there, sometimes people get very, very micro-managerial about other people's creative process.