The 5yr thing is to prevent accounting gimmicks for FFP I believe, between the player and the club there's still an 8 year deal. That has benefits like not losing players on a free, retaining value etc. (Woodward must be super frustrated with himself that he didn't think it up somewhere).
Paying the transfer fee and depreciating ( amortisation of the fee ) aren’t the one and the same.
There are of course pitfalls in offering a player a long term contract but from an accounting point of view it is a valid approach but also those long contracts do set out wages or terms for the whole period
I can’t recall where I saw it but it was quite surprising just how few players didn’t either 1) sign a contract extension 2) were sold before the contract ended as opposed to how few when a fee over £10 million was paid saw their initial contract to its end.
As an aside it was rumoured that UEFA were going to limit the period that a few could be amortised over from this window on. I can’t see that this change has been sanctioned yet and with the window now being open I wonder if any one has actually see that either at PL level or indeed UEFA level it’s been changed