If we buy him (hypothetical) on a four year deal at £20m, that's £5m a year? Yes.
If we loan him for a year at £5m, and the repeat three times, that's £20m too (Hypothetical, I know).
The ever so slight difference between the two is that if we BUY him, we can at some point SELL him to recover some of the outlay. You can't sell a player that has been loaned to you by another club, so you cannot recover the outlay.
Did you really not think of that yourself?
Im working on the basis of him seeing out his contract, then walking.