Obviously the ideal situation would be to never promote someone who will abuse their power. Unfortunately, that requires a pretty deep and intimate knowledge of other people. And this is, well, you know... The internet. No matter how well you think you know your internet BFF5EVAOMG - you don't. You might know them better than other people on the game, and you actually might know them pretty well, but simply by virtue of meeting someone on the internet you already don't know them. So you're left with a choice - trust someone you don't really know, or don't trust anyone. Lets look at those.
Trust someone you don't really know. This is what most people end up doing, and it makes sense. If you're leading a team (of however many people can be on a team now, still 100?) there are going to be a lot of people on, and you can't always be on (inb4 nolyfer objects). If you want your rules and ideals to be enforced at all times you either have to never log off (please... don't do this) or you're going to have to trust others to enforce your rules and ideals.
Don't trust anyone. This leads to either nolyfing so everyone follows your rules, or just accepting that things might happen that you don't like while you're offline. Then it becomes a he-said she-said situation if/when a problem occurs.
In conclusion - transparency is good. It makes people accountable, and helps explain otherwise unexplainable things. Nor should this be particularly hard to implement. While I don't know how PokeMMO implements messages, I'm assuming its something sort of like
team.sendMessage("User %s has left the clan", User1);
and could be easily changed to
team.sendMessage("User %s was kicked from the clan by %s", User1, User2);