part of the reason the guide uses development for players is that it is automatically one of the most expensive upgrades to get, While, also making it so that players can get experience faster. A Slow player has to be a player that can break records constantly til you get him up in development. His weekly xp gains from goals are less than half of what they could be. So it takes way longer to even get development up to where he could be leveling quickly. Now the only thing that I want to re-emphasize is that WITH the coaches xp upgrade for positions, you only need players to be quick development to get the full xp from weekly goals. However being superstar still makes their season goals more reachable.