What is the difference between, ignoring wages:
a) us buying player A for 3 million right now on a three year deal, with him leaving at the end of his contract
b) us paying 1 million in loan fees for players X, Y and Z in each of the 22/23, 23/24 and 24/25 seasons?
The answer is there is none. The only benefit with buying permanently is that you either hope the player develops rapidly and will appreciate in value which you can then exploit by selling on, which happens basically never for older players, or that you can get the player to extend their contract without taking the piss massively in improved wages/agent fees.