I get that, but unfortunately it was simplified in a way that actually obscures how amortization works in the short and long term. Wages often matter as much, if not more than, the amortisation of the transfer cost. Sancho's wages over the course of his contract, for instance, significantly exceeds his transfer sum. Also, it obscures a further fairly key point, which is that there are very significant costs to bringing in a new player that you don't get when you're just keeping one (agent fees etc). This is how you ended up arguing that selling Greenwood for 25m would enable buying someone else for 125m in terms of FFP impact next season, when the reality would be that it might enable you to buy someone maybe half that price.
And again, even in the short term there's not a very clear case that you get a better FFP outcome from selling Sancho and buying someone else than you do by just keeping him. Which was the point I responded to. People assume that because he's an academy product, it's lucrative in FFP terms to sell him. But it really isn't - unless you don't have to replace him.