Dumfries and Skiniar kinda shows why I don't like the buy youngster and sell them for profit in the future approach, on paper it sounds so good, but in reality this is the trend.
Even Mabappe pocketed the €150m signing fee; like what does Oaktree think the youngster are? back in the 90s being clueless, do what you say? Ajax, Arsenal model?
Even the Barca model cannot work like that, hence they needed to overpay the players to retain them, then you might have a chance of selling a few of them with high price, but not exactly high profit, cause the increase of expense.
The most practical and healthy approach should be acknowledging the salary and transfer/signing (acquiring) fees is the expense of operating; and within the service period time, hopefully with other elements can bring us profit through competition performances, recognition increases; and the profit from transfers are just windfalls.
In another perspective the transfer fees are kinda asking charity from the player, as it is very tied to the potential income they can gain from the next employer for their future services elsewhere. It should be looked as a compensation of breaking a contract, but not trying to gamble by signing a lots of contracts and paying up front and hope some of them will be breached in order to make a profit.