The whole issue here is not really about so-called rules. At this point no one is saying City have done anything illegal. But have they broken the PL's own internal rules? Let's wait and see.
But the main issue here is why has there been selective action taken by the PL against City. For example how many players in the PL have had image right deals? Probably scores, perhaps hundreds. Most clubs do it as way of helping players reduce their tax payments. It's not very nice but tax avoidance is legal. We have heard about the huge offshore image right firms used by Ronaldo and Pogba for instance. It all looks a bit dodgy. So how many investigations have been made into other clubs' image rights deals by the PL? The answer is zero. That tells you the rules are not rules at all.