A factor that plays into the outrage is the fact that the mounts cost gems instead of gold. Since you can easily swap between gems and Gold the currencies are essentially interchangeable extept of how they feel. An item that costs a lot of gems feels like a ripoff. An item that costs a lot of gold feels prestigeous. Keep the microtransactions to the micro scale. I'd go to back the original stables of the mounts and add an npc that sells mount skins at a price of 60g for the more plain skins and 90-120 gold for the more intricate ones. Like this, the players can easily get a non-default skin on the cheaper side and a high flash-factor skin as a long term goal. And honestly with 5 mounts in the game, many will resort to exchange gems for gold instead of paying 60-120 gold five times over. But that's just my prediction