That's the AFL landscape these days. GC can make it as difficult as they like, but the reality is that as long as players (and especially elite youngsters) want to leave the club, they will often find themselves in a situation where they can't get full value for the player. The successful clubs tend to allow players to leave their club, even when they don't get full value, but they also create an environment where elite players don't want to leave year in year out. GC taking a stand is admirable, but the problem is that once a player decides they want out, the club has already lost the battle, regardless of whether they get a good trade.
GC can talk all they want about wanting to get mature players, but until they can convince players to actually go there, it's nothing but a distraction. They have picks 4, 6, 8, and could have 10, and yet the only players they can convince to come to their club are Hanley and Lyons? Some combination of those picks would be more than enough to satisfy another club in a trade for an elite player, or at least a very high level player, yet GC have been unable to get any of those players to want to come to the club. And that's where GC have to take advantage of the current situation. There is nothing stopping them from poaching players from other clubs, and forcing those clubs to trade players for less than their value.