This is true but I'd imagine it making more sense being more based on the players individual success, ie Arsenal appearances, goals/assists, Balon Dor nomination, Balon Dor winner, sell on clauses.
Yes, but those are the types of add-ons we'd want (Arsenal). Add-ons that sound fair, but aren't literally all going to trigger one after the other in the span of 6-12 months.
You can only imagine the kinds of add-ons they want. They would want very obvious, easy to hit objectives that they know will hit, and hit soon, trying to turn the add-ons basically into defacto guaranteed payments.
Thus, the negotiations taking time.
Because many deals these days say £Xm + £xm in add-ons, but very rarely do we as fans ever find out what all those add-ons are, unless they come close to triggering or a well-sourced journalist or outlet reports on them.
For example. most people didn't know Grealish had a release clause until the summer City bought him.